# Animal Anatomy

Abducens
The Abducens (or Sixth Cranial Nerve) rises in the medulla oblongata and supplies the external rectus muscle of the eye, which draws the eyeball outward.

Abducent nerve
see "Abducens"

Accessory nerve
The accessory nerve is a pair of cranial nerves responsible for the sternomastoid and trapezius muscles.

Acetabulum
Acetabulum is an anatomical term applied to any cup-like cavity, as that of a bone to receive the protuberant end of another bone.

Achilles Tendon
The Achilles Tendon is the tendon which connects the heel with the calf of the leg, and is the principal extensor of the foot.

Adam's Apple
Adam's Apple is the popular name for the thyroid cartilage. That is the prominence seen in the front of the throat of man. It is small and invisible in females. It is so called from the notion that a piece of the forbidden fruit stuck in Adam's throat.

Adenoids
Adenoids is the pathological enlargement of the lymphoid tissue, arranged as a series of folds behind the opening of the auditory tube in the nasopharynx; also known as the pharyngeal tonsils.

Adipose tissue
Adipose tissue is a form of connective tissue in which the constituent cells are modified to enable them to contain droplets of oil. (Fat).

Adrenal glands
The adrenal glands are a pair of glands on the kidneys which secrete adrenaline and other hormones.

Alimentary
The alimentary canal is the channel in an animal through which food passes.

Alveoli
see "Alveolus"

Alveolus
An alveolus is a lung air sac where gas exchange with the blood occurs.

Amitosis
Amitosis is the anatomical term given to cell reproduction by direct division. The nucleus becomes constricted in the middle, forming an hour-glass shape and then divides into two. This is followed by a division of the whole protoplasmic mass of the cell; two daughter cells are thus formed, each containing a nucleus. Direct division occurs in leukocytes and bone-cells, and in the epithelial cells lining the urinary bladder.

Amnion
The amnion is a membranous sac which surrounds the embryo; it is developed in reptiles, birds and mammals, but not in amphibia or fishes.

Amygdala
The amygdala is an almond-shaped region of the brain adjacent to the hippocampus, that links the cortex, responsible for conscious thought, with the regions controlling emotions. A 1994 American study showed that it was involved in interpreting fear-provoking information and linking it to fear responses. For example, where the amygdala is damaged patients are unable to recognize fearful expressions.

Anaphase
Anaphase is the 3rd stage of mitosis cell reproduction. The centromeres split into 2 halves which repel each other.

Anatomy
Anatomy describes the structure and organisation of living creatures.

Anconeus
The Anconeus is a muscle in the human arm. It assists the Triceps in extending the elbow-joint.

Ankle
The ankle is the joint connecting the foot with the leg.

Antenna
An antenna is a sensory organ found on the head of insects.

Antibody
An antibody is a bodily protein that inactivates infection.

Anus
The anus is the opening at the end of the alimentary canal.

Aorta
The aorta is the largest artery in the human body. It carries blood from the heart to the arms, legs and head.

Aqueous humour
The Aqueous humour is the watery fluid found in the space between the cornea and the lens of the eyes of vertebrates.

Areolar tissue
Areolar tissue is a generalised form of connective tissue in which the constituent cells are separated by a semi-fluid matrix in which both white connective tissue and yellow elastic fibres are found.

Arm
The arm is a limb extending from the shoulder of an animal.

Artery
An artery is a vessel that conveys blood from the heart.

Atlas
In anatomy, the 1st cervical vertebrae is called the atlas because it supports the globe of the head.

Auricle
The auricles are reservoirs within the heart which receive blood from the veins.

Axis
In anatomy, the 2nd cervical vertebrae is called the axis. It provides the pivot for the atlas and the head.

Basophils
see "Leukocytes"

Biceps
The biceps are a long fusiform muscle on the front of the arm. They are used to flex the elbows.

Bile
Bile is a secretion of the liver stored in the gall bladder.

Bladder
The bladder is a sack in the abdomen which collects urine from the kidneys.

Blood
Blood is a body fluid that carries food and oxygen to cells.

Blubber
Blubber is the thick coating of fat enveloping whales.

Bone
Bone is the hard skeletal part of an animal.

Bowel
The bowels is a popular term for the division of the alimentary canal below the stomach, that is the intestines.

Bowels
see "Bowel"

Brachialis
The Brachialis is a muscle covering the front of the human elbow-joint. It is used to flex the elbow.

Brain
The brain is the central organ of the nervous system.

Bronchi
The bronchial tubes (bronchi) are a division of the trachea which branch repeatedly into small bronchioles within the lungs.

Bronchial
see "Bronchi"

Buccinator
The buccinator is a flat thin muscle of the cheek. It compresses the cheeks and retracts the angle of the mouth, thereby assisting mastication and regulating the expulsion of air in whistling or playing a wind-instrument.

Calcaneum
In human anatomy, the calcaneum is the largest and strongest of the tarsal bones. It projects backwards beyond the bones of the leg to provide a lever for the muscles of the calf.

Capillary
A capillary is a fine blood vessel which carries blood to cells.

Capitate bone
The capitate bone is the largest bone in the human wrist.

Carpus
The carpus are the bones of the human wrist.

Cartilage
Cartilage or cartilaginous tissue covers the ends of the bones where they come together to make a joint. It enables the bones to move easily.

Cartilaginous joint
In anatomy, a cartilaginous joint is an articulation where the bones are joined by cartilage, and a limited amount of movement is possible.

Cartoid
see "Cartoid Artery"

Cartoid Artery
The Cartoid Arteries are three arteries on each side of the human neck. The term Cartoid Artery is usually applied to the common cartoid artery, which is the vessel injured when the throat is cut. Compression of the cartoid arteries causes fainting from anaemia of the brain.

Cartoids
see "Cartoid Artery"

Cell
A cell, in biological terms, is the material unit of all living things.

Cephalic
Cephalic is a classification of human skull. It refers to the shape of skull possessed by Kaffirs and Native Australians.

Cerebellum
The cerebellum is the lower part of the brain, it controls muscular movements and postural equilibrium.

Cerebrum
The cerebrum is the upper and larger portion of the brain and occupies the whole of the dome of the cranium.

Cervical vertebrae
The cervical vertebrae are the 7 vertebrae closest to the skull.

Cervix
see "Cervix uteri"

Cervix uteri
The cervix uteri (cervix) is the neck of the womb. It is the part of the uterus that projects into the upper part of the vagina. It is a powerful ring of muscle which is closed at most times but is able to expand (dilate) widely during childbirth.

Chitin
Chitin is an organic substance which forms part of the exoskeleton of arthropods.

Cilia
Cilia are hair-like processes of the cells of some animal tissues, or of a single cell in some Protozoa. Their function is to keep fluids moving in one direction by their sweeping action, or to affect locomotion.

Clavicle
In human anatomy, the clavicle is a long bone which lies almost horizontally at the root of the neck. It serves 2 main functions; to act as a prop which braces back the shoulder and enables the limb to swing clear of the trunk. And to transmit part of the weight of the limb to the axial skeleton.

Coccyx
In human anatomy, the coccyx is the bone at the apex of the sacrum. It is usually comprised of 4 vertebrae fused together.

Collagen
Collagen is one of the albuminoids. It forms the white fibres of connective tissue.

Colon
The colon is the large intestine.

Connective tissue
Connective tissue is derived from the mesenchyme and includes a number of tissues which have a passive, binding function. In a connective tissue the parent cells are separated more or less widely from one another by a homogeneous matrix or ground substance, in which fibres may or may not be present.

Coracobrachialis
The Coracobrachialis is a human muscle used to draw the arm forwards and prevent side-sway when the arm is raised by the Deltoid.

Coracoid Bone
In birds, the Coracoid Bone is the bone joining the sternum to the shoulder and supporting the wing. In mammals it is represented by the coracoid process of the scapula.

Costal Cartilages
In human anatomy, the costal cartilages are bars of hyaline cartilage which extend forwards from the anterior ends of the ribs and contribute to the elasticity of the thorax.

Cranial nerve
A cranial nerve is a nerve arising directly from the brain and passing through one of the holes in the skull. There are twelve pairs of cranial nerves: Olfactory, Optic, Oculomotor, Trochlear, Trigeminal, Abducent, Facial, Auditory, Glossopharyngeal, Vagus, Accessory and Hypoglossal.

Cuneiform bones
The cuneiform bones are three bones in the human foot behind the first three metatarsal bones.

Cuticle
The cuticle is the horny outside layer of skin.

Decidua
The decidua is the lining of the uterus, shed during a menstrual period and after the birth of a child.

Deltoid
The deltoid muscle is a triangular muscle in the shoulder used to lift the upper arm. The base of the triangle is attached to the clavicle and the scapula; the fibres converge on the narrow apex half-way down the outer side of the humerus.

Dentin
see "Dentine"

Dentine
Dentine (dentin) is the main substance of the tooth.

Desmology
Desmology is the branch of anatomy dealing with ligaments and sinews.

Detrusor urinae
The detrusor urinae is the muscle whose function it is to expel the urine.

Dew-claw
Dew-claw is the name given to the upper-most claw in a dog's foot which is smaller than the rest and does not reach the ground. The name is also applied to the bones behind a deer's foot.

Diaphragm
The diaphragm is a large transverse muscle at the base of the thorax, used in respiration to draw air into the lungs.

Diploe
Diploe is the anatomical term for the spongy substance between flat bones.

Duodenum
The duodenum is the first part of the intestine.

Dura Mater
The dura mater is the membrane which covers the brain.

Ear
The ear is the organ used for hearing. It converts sound into electrical impulses that are fed to the brain.

Eggs
see "Egg"

Elastic tissue
Elastic tissue is ordinary connective tissue with the addition of many fibres of the albuminoid elastin. It resembles draper's elastic and is found in some ligaments and in the walls of the arteries.

Elastin
Elastin is one of the albuminoids. It forms the yellow fibres of connective tissue.

Endocrine gland
An endocrine gland is one which secretes hormones into the body.

Endocrine System
The Endocrine System is a number of separate glands differing in structure and function, but all characterised by the fact that they have no ducts through which to discharge their secretions; but instead discharge them straight into the blood-stream. These secretions are called hormones or sometimes endocrines.

Endogenous
Endogenous refers to the structure of the vascular system, which consists of strands of ligneous tissue isolated in a cylinder of cellular tissue. The term is used to describe the Monocotyledonous group of plants.

Epidermis
The epidermis is the outer layer of an animal's skin.

Epiglottis
The epiglottis is a fibro-cartilaginous lid shaped like a leaf which covers the upper opening of the larynx. It is covered by a mucous membrane and contains taste and mucous glands.

Epithelium
Epithelium is an anatomical term a basic type of bodily tissue. It comprises the external surface of the skin, the internal surfaces of the digestive, respiratory and urogenital systems and others. The constituent cells of an epithelium are always closely packed together and the intercellular substance is reduced to a minimum.

Erythrocyte
Erythrocyte is the anatomical term for red corpuscles.

Erythrocytes
Erythrocytes (red blood cells) are haemoglobin-containing blood cells present in most vertebrates. Their main function is the transportation of oxygen and carbon dioxide in the blood.

Exocrine gland
An exocrine gland is one which secretes onto a surface. Such as a sweat gland.

Eye
The eye is the organ of vision.

Fallopian tubes
The Fallopian tubes are two tubes in mammals which carry eggs from the ovary to the uterus. Eggs are fertilised in the Fallopian tubes by sperm, and then moved to the ovary by way of cilia.

Femur
The femur is the thigh bone in the human leg.

Fibrous joint
In anatomy, a fibrous joint is an articulation in which the surfaces of the bones are fastened together by intervening fibrous tissue, and in which there is no appreciable motion, as in the joints between the bones of the human cranium.

Fibrous Joints
In anatomy, fibrous joints are articulations in which the surfaces of the bones are fastened together by intervening fibrous tissue, and in which there is no appreciable motion. For example between the bones of the cranium.

Fibula
The fibula is the lateral bone of the leg. It is slender, compared to the tibia. It's purpose is to give attachment to the muscles.

Flagellum
Flagellum are a small hair-like organ on the surface of certain cells. They are the motile organs of the sperm cells of higher animals.

Flat bone
In human anatomy, flat bones occur where the principal requirement of the skeleton is to protect delicate structures or provide broad surfaces for muscular attachment. The bones are comprised of two thin layers of compact bone separated by a variable quantity of spongy substance.

Flat bones
In human anatomy, flat bones provide protection and a broad surface for muscular attachment. They are formed of two thin layers of compact bone separated by a spongy substance.

Foetus
A foetus is an unborn offspring of an animal.

Follicle
A follicle is a small group of cells that surrounds and nourishes a structure such as a hair (hair follicle) or a cell such as an egg (Graafian follicle).

Fontanelle
The fontanelle is a membrane covered vault in the skull. It normally closes during infancy.

Fovea
The fovea is a small depression in the retina where vision is most acute.

Frontal bone
The frontal bone is the plate at the front of the top of the human skull. It forms the forehead.

Gall Bladder
The gall bladder is a small muscular sac attached to the liver.

Ganglion
A ganglion is an enlargement occurring somewhere in the course of a nerve, and containing nerve cells in addition to nerve filaments.

Gastric Juice
Gastric Juice is a clear, colourless fluid secreted by the mucous membrane of the stomach, and is the chief agent in digestion.

Gastric System
The Gastric System refers to all parts of the body which contribute to digestion.

Gastrocnemius
The Gastrocnemius is a muscle forming most of the human calf.

Gills
Gills are a respiratory organ found in animals which obtain oxygen from water, such as crustaceans, molluscs, fish and amphibians.

Gingiva
see "Gums"

Gizzard
The gizzard is a strong muscular part of a bird's alimentary canal which enables them to grind their food. Gizzards also occur in many gastropods, and in certain cephalopods and crustaceans.

Gland
A gland is a bodily organ that manufactures and secretes enzymes, hormones or other chemicals.

Gluteus maximus
The Gluteus maximus is a large muscle in the human back-side.

Gnathic
Gnathic is a classification of human skull shape found in Europeans.

Graafian Vesicles
The Graafian Vesicles are numerous small globular transparent follicles found in the ovaries of mammals. Each follicle contains one ovum which is expelled when it reaches maturity.

Gums
The gums (gingiva) are firm fleshy tissue covering the alveolar parts of either jaw and enveloping the necks of the teeth.

Haemoglobin
Haemoglobin is the protein that carries oxygen in the blood.

Hallux
The hallux is the innermost of the five digits which normally compose the hind foot of a vertebrate. In humans the big toe, in a bird the hind toe.

Hamate bone
The hamate bone is one of the bones in the human wrist.

Haversian Canals
The Haversian Canals are a network of minute canals, which traverse the solid substance of bones and proceed from the central cavity. They convey nutrient vessels to all parts.

Heart
The heart is the muscle in vertebrates which pumps blood around the body.

Hormone
A hormone is a product of the endocrine glands.

Humerus
The humerus is the long bone in the upper region of the human arm. It joins with the shoulder at the glenoid cavity.

Hypoglossal nerve
The hypoglossal nerve is a pair of cranial nerves responsible for the movements of the tongue.

Hypothalamus
The hypothalamus is the region of the human brain below the cerebrum which regulates rhythmic activity and physiological stability within the body, including water balance and temperature.

Ileum
The ileum is a continuation of the jejunum and opens into the colon.

Iliacus
The Iliacus is a muscle in the human thigh.

Insulin
Insulin is a hormone produced by the pancreas and released into the bloodstream. It promotes the uptake of glucose from the blood by the body cells. A lack of insulin results in glucose being neither consumed as fuel nor adequately stored, but instead the glucose accumulates in the blood until it spills over into the urine. An excess of insulin dangerously decreases the amount of glucose in the blood.

Intercostal
Intercostal is a latin term meaning 'between the ribs' and refers to muscles etc which are present between any two ribs.

Interferon
Interferons are proteins formed in the body it is thought in response to viruses and other agents, including some bacterial toxins, however, they're precise function is as yet still unproved.

Interossei
Interossei are muscles in the human hand and foot.

Intestine
The intestine is the convoluted membranous tube which extends from the stomach to the anus and which receives the ingested food from the stomach, mixes it with bile, pancreatic juice and intestinal secretions, gives origin to the chyle and delivers the indigestible products from the system.

Intestines
see "Intestine"

Irregular bones
In anatomy, irregular bones are bones which do not fit into any of the other bone types. They are comprised of a spongy substance enclosed within a thin layer of compact bone.

Jejunum
The jejunum is the second part of the human small intestine. It is about 9 feet long.

Joint
A joint is a structure where two bones meet.

Jugular vein
The jugular vein returns blood from the head to the heart in vertebrates.

Kidney
The kidney is a gland used for filtering urine from the blood.

Kidneys
see "Kidney"

Labrum
The labrum is the ventral lobe in the front of an insect's head which covers the mouth parts.

Lachrymal gland
The lachrymal gland is a gland beneath the upper eye lid which secretes tears which drain from the inner corner of the eye through the Lachrymal duct to the nose.

Lacteals
Lacteals are small lymphatic vessels which arise from the mucous membrane lining of the small bowel.

Lambdoidal suture
The lambdoidal suture is a fissure which divides the parietal bone from the occipital bone in the human skull.

Larynx
The larynx is a cavity at the top of the trachea containing the vocal cords.

Leukocyte
Leukocytes is the anatomical term for colourless corpuscles. (White blood cells).

Leukocytes
Leukocytes (white blood cells) are colourless bodies, larger than red blood cells. There are several types of leukocytes the purpose of which is not clear, however, one type, the neutrophils, act as scavengers engulfing and destroying invading bacteria. Another type, the basophils inhibit the clotting of the blood.

Lip
The lips are the fleshy edges of the opening of the mouth.

Liver
The liver is the largest gland in the human body. The liver has three functions: it secretes bile, stores glycogen and converts waste products into urea and uric acid for excretion.

Long bones
In human anatomy, long bones are found in the limbs where they form levers. They have a hollow shaft.

Longus capitis
The longus capitis is the human muscle which flexes the head.

Longus cervicis
The longus cervicis is the human muscle which bends the cervical portion of the vertebral column forwards.

Lumbar vertebrae
In human anatomy, the lumbar vertebrae are the 5 vertebrae following the thoracic vertebrae.

Lumbricals
The Lumbricals are muscles in the human fingers used in writing etc.

Lunate bone
The lunate bone is one of the bones in the human wrist.

Lung
see "Lungs"

Lungs
The lungs are organs used for respiration.

Malleus
The malleus is a small bone in the middle ear which transmits sound vibrations from the tympanum to the incus.

Mandible
In human anatomy, the mandible is the bone at the front and bottom of the skull (lower jaw).

Masseter
The masseter is the human muscle which moves the mandible for chewing.

Maxilla
The maxilla is the bone comprising the upper jaw in the human skull.

Maxillae
The maxillae form the upper jaw of the human skull.

Maxillary artery
In human anatomy, the maxillary artery is the larger terminal branch of the external cartoid artery. It rises behind the neck of the mandible and is at first imbedded in the partoid gland. It passes forwards between the neck of the mandible and the sphenomandibular ligament and then to the Lateral pterygoid and enters the pterygopalatine fossa between the two heads of that muscle.

Mentalis
The mentalis is a muscle in the human face, it raises and protrudes the lower lip and wrinkles the skin of the chin.

Mentum
In anatomy, the mentum is the anterior and inferior mandible of the lower jaw.

Metacarpal
see "Metacarpus"

Metacarpus
The metacarpus are the five bones of the human palm.

Metaphase
Metaphase is the 2nd stage of mitosis cell reproduction. The chromosomes have become irregular V shaped and arrange themselves around the equator.

Metatarsal
see "Metatarsus"

Metatarsus
The metatarsus are the 5 bones in the anterior part of the human foot. They are between the tarsus and the phalanges.

Mitosis
Mitosis is cell reproduction by indirect division. It is the common method of division in the higher animals. It is characterised by a series of complex changes in the nucleus leading to its subdivision. The process takes between 30 minutes and a few hours, and is comprised of 4 stages: prophase, metaphase, anaphase and Telophase.

Mucin
Mucin is a protein and the principal constituent of mucus.

Mucous
Mucous is a term for surfaces which secret or are covered with mucus.

Mucus
Mucus is a thick fluid secreted by mucus membranes in animals. It acts as a protective barrier, lubricant and a carrier of enzymes.

Nasal
Nasal is a classification of human skull shape found in primarily in Negroes.

Neck
The neck is the part of the body which connects the head with the shoulders.

Nerve
The nerves are a part of the body which generate and transmit electrical impulses.

Neutrophils
see "Leukocytes"

Nose
The nose is an animal's organ of smell.

Occipital bone
The occipital bone is the plate forming the back of the human skull.

Occipitofrontalis
The occipitofrontalis is the broad muscle of the human scalp.

Oesophageal
Oesophageal is a secretion from the membrane of the oesophagus. It is a mucus lubricant to assist peristalsis.

Oestrogen
Oestrogen is a hormone produced in the ovary of a vertebrate.

Omentum
The omentum is a long fold of the peritoneum. It is loaded with fat and lies in front of the bowels in the abdominal cavity. It protects the bowels and keeps them warm.

Orbicularis oculi
The orbicularis oculi is the broad, flat, elliptical muscle which occupies the human eyelids and spreads down towards the cheek.

Orbit
In human anatomy, the orbits are a pair of roomy cavities in the skull which contain the eyes.

Orbital
Orbital is a classification of human skull shape and refers to the skulls of Tasmanians.

Orbital opening
The orbital openings are the eye-sockets in the human skull.

Os calcis
The Os calcis is the heel bone of the human foot.

Ossein
Ossein is one of the albuminoids. It is the chief organic constituent of bone. Chemically it is similar to collagen.

Osseous tissue
see "bone"

Palatine bones
The palatine bones are part of the floor of the nasal cavity and the roof of the mouth in the human skull.

Pancreas
The pancreas is an elongated secreting gland which secretes pancreatic juice and insulin.

Parathyroid Glands
The parathyroid glands are two small glands in the neck concerned with the use of calcium in the body.

Parietal bone
The parietal bone is the plate on the top of the human skull, comprising most of the dome of the skull.

Parietal bones
The parietal bones form the sides and the roof of the human cranium.

Patella
The patella is the largest of the sesamoid bones. It is situated in front of the knee-joint. It is a flattened, triangular bone.

Pectineus
The Pectineus is a muscle in the human thigh.

Pelvis
The pelvis is a bony girdle in vertebrates that connects the body with the lower extremities.

Pericardium
The Pericardium is a conical, fibroserous sac containing the human heart and the roots of the major veins and arteries.

Phalange
The phalanges are the bones of the human digits (fingers).

Piriformis
The Piriformis is a muscle in the human hip.

Pisiform bone
The pisiform bone is one of the bones in the human wrist.

Pituitary gland
The pituitary gland is a gland within the brain concerned with regulating growth and regulating other ductless glands.

Placenta
The placenta connects a foetus to the uterine wall. It is the organ by means of which the nutritive, respiratory and excretory functions of the foetus are carried on.

Plantais
The Plantais is a muscle in the leg.

Plasma
Plasma is the liquid part of the blood.

Platysma
The platysma is a neck muscle in the human body.

Procerus
The procerus is a muscle in the human nose.

Progesterone
Progesterone is a hormone that regulates the menstrual cycle in vertebrates.

Prophase
Prophase is the 1st stage in mitosis cell reproduction. The nucleolus disappears and a number of chromosomes become apparent.

Prothrombin
Prothrombin is a substance in the plasma from which thrombin is derived during blood clotting.

Pulmonary Artery
The pulmonary artery opens out of the right ventricle in the human heart and conveys venous blood to the lungs for collecting oxygen.

Quadrate Bone
The Quadrate Bone is a bone developed in reptiles and birds by means of which the lower jaw is articulated to the skull.

Radius
The radius is one of the two long bones which form the human lower arm.

Rectum
The rectum is the lowest portion of the large intestine, terminating at the anus.

Red Blood Cells
see "Erythrocytes"

Rib
In anatomy, the ribs are elastic arches of bone which are connected behind with the vertebral column and form a large part of the skeleton of the thorax.

Sacrum
In human anatomy, the sacrum is the large triangular bone inserted like a wedge between the two hip bones. It is formed by the fusion of the five sacral vertebrae.

Sagittal suture
The sagittal suture is the fissure running along the length of the top of the human skull dividing the parietal bone into two hemispheres.

Saliva
Saliva is a secretion from the salivary glands in the oral cavity. It contains mucus to lubricate food and enzymes.

Scaphoid bone
The scaphoid bone is one of the bones in the human wrist.

Sciatic
The sciatic is a nerve in the leg.

Sclerous tissue
Sclerous tissue provides the stiffening which is essential for the formation of the general framework of the body. There are two varieties of sclerous tissue: cartilage and bone.

Sebaceous glands
The sebaceous glands are ducts in the skin which secrete oil to lubricate the skin and hair.

Secretin
Secretin is a hormone produced by the small intestine in vertebrates that stimulates the production of digestive secretions.

Semitendinosus
The Semitendinosus is a muscle in the human thigh.

Septum
A septum is a muscular partition separating the two sides of the human heart.

Short bone
In human anatomy, short bones occur where the skeleton is intended for strength. Short bones consist of a spongy substance surrounded by a thin crust of compact bone.

Short bones
In human anatomy, short bones are part of the skeleton designed for strength and compactness. They are comprised of a spongy substance surrounded by a thin crust of compact bone.

Sinus
A sinus is an air-filled space in the diploe of a skull bone.

Sixth Cranial Nerve
see "Abducens"

Skeleton
The skeleton is the hard internal or external framework of bones, cartilage or shell which provides protection for an animals organs, provides fixing points for the muscles and a general frame for the body.

Skin
In the human body, skin, or Dermoid Tissue, is composed of two layers, the cuticle, epidermis or epithelium and the corium or dermis.

Sphenoid bone
The sphenoid bone is situated at the base of the human skull, in front of the temporal bones and the basilar part of the occipital bone.

Spinales
The spinales are human muscles which extend the vertebral column.

Spine
Spine is a popular term for the vertebral column (spinal column).

Spleen
The spleen is an organ of vertebrates that regulates the number of red blood cells.

Splenii
The splenii are two muscles in the human body, the splenius capitis and the spelnius cervicis. They are used to move the head backwards, to one side and to rotate it.

Splenius capitis
see "Splenii"

Splenius cervicis
see "Splenii"

Stenson's Duct
Stenson's duct is the duct leading from the parotid gland to the inside of the cheek, where it discharges saliva.

Sternocostalis
The sternocostalis is a muscle in the human body.

Sternohyoid
The sternohyoid is a muscle in the human body which depresses the hyoid bone.

Sternomastoid
The sternomastoid is a muscle in the human neck.

Sternum
In anatomy, the sternum is a long flat bone which forms the median portion of the anterior wall of the thorax. The top of the sternum supports the clavicles.

Subclavius
The Subclavius is a muscle in the human body between the clavicle and the first rib. It steadies the clavicle during movements of the shoulder.

Sublingual Glands
The sublingual glands are salivary glands in the floor of the mouth, close under the mucous membrane, one on either side of the fraenum of the tongue. they secret saliva through numerous ducts of Rivini, some of which unite to form the duct of Bartolin.

Supinator
The Supinator is a muscle surrounding the upper one-third of the radius in the human arm. It is used to rotate the radius, thereby turning the palm of the hand forwards.

Suture
A suture is an anatomical term for an articulation found only in the skull, where the margins of the bones articulate with one another, but are separated by a thin layer of fibrous tissue (sutural ligament) and is continuous externally with the periosteum on the outside of the skull and internally with the fibrous layer of the dura mater.

Synovial joint
In anatomy, a synovial joint is one where the bones are covered with articular cartilage but are not attached to each other. These joints allow extensive movement.

Synovial Membrane
In anatomy, a synovial membrane is a thin, delicate membrane, secreting a thick viscid and glairy fluide like egg-white. Synovial membranes are arranged in the form of short, wide tubes around joints as the lining of synovial bursae, and as sheaths for tendons.

Talus
In human anatomy, the talus is the principle connecting link between the foot and the bones of the leg and has an important part in the formation of the ankle.

Tapetum
The tapetum is the irregular sector in certain animal's eyes which shines owing to an absence of black pigment. Tapetum is found in the eyes of cats.

Tarsal
see "tarsus"

Tarsus
In human anatomy, the tarsus comprises 7 short bones which make up the skeleton of the posterior half of the foot.

Teat
The teat is the small protuberance at the tip of the breast of female mammals upon which the ducts of the mammary gland open to supply milk to the suckling young.

Telophase
Telophase is the 4th stage of mitosis cell reproduction. The nuclear membrane and the nucleolus reappear and the cytoplasm undergoes constriction around the equator of the achromatic spindle. The constriction deepens and the original cell is gradually divided.

Temple
In anatomy, the temple is the flat part either side of the head between the forehead and the ear.

Temporal bones
The temporal bones are situated at the sides and base of the human skull. They assist in the protection of the cerebrum and the transmission of sound waves to the ear.

Temporalis
The temporalis is the human facial muscle which raises the mandible, closing the mouth.

Tendon
A tendon is a connective tissue that joins muscles to bone in vertebrates.

Tensor
A tensor is a type of muscle which tightens or stretches a part of the body.

Testes
Testes is the plural of testis.

Testicle
Testicle is another name for testis.

Testis
The testis is the male organ in which sperm are produced. Most mammals have two testis enclosed in the scrotum.

Testosterone
Testosterone is the male sex hormone secreted by the testes.

Thalamus
The thalamus is the interior region of the brain where certain important sensory nerves, especially the optic nerve, originate.

Theca
In anatomy, a theca is a case or sheath which encloses some organ or part.

Thenar
The thenar is the ball of muscle at the base of the thumb.

Thoracic Duct
The thoracic duct begins in the abdomen, close in front of the spinal column at the level of the second lumbar vertebra, as the receptaculum chyli, and running upwards to the root of the neck curves a little to the left, and arches over to empty itself into the venous blood-stream at the junction of the left internal jugular and subclavian veins.

Thoracic vertebrae
In anatomy, the thoracic vertebrae are the 12 vertebrae following from the cervical vertebrae. They provide articulation for the ribs.

Thorax
The thorax in vertebrates is the part of the body containing the heart and lungs and protected by the rib cage.

Thymus
The thymus is a ductless glandular body situated near the base of the neck in vertebrates. Its function is uncertain, and in man it disappears or diminishes soon after childhood.

Thyroid
The thyroid is an endocrine gland near the larynx in vertebrates. It influences growth and development.

Thyroid gland
see "Thyroid"

Tibia
The tibia is the medial and stronger of the two bones of the leg. It is prismoid in form, and possesses a shaft and two ends. Its purpose is to support the weight of the body.

Tibiotarsus
In birds, the tibiotarsus is the equivalent of the tibia, but it is fused at the lower end with some of the bones of the tarsus.

Tongue
The tongue is a muscular organ in the mouth of a tetrapod.

Tonsils
The tonsils are a pair of small organs on either side of the root of the tongue composed of lymphatic tissue and instrumental in protecting the throat from infection.

Tooth
A tooth is a hard structure in the mouth of vertebrates.

Trachea
The trachea (windpipe) is a nearly cylindrical tube, composed of cartilagious and membraneous tissues, and extending downwards from the lower part of the larynx to the level of the third dorsal vertebra, where it bifurcates into the two bronchi. It lies upon the oesophagus posteriorly, and is in relation with the cartoid arteries, the thyroid gland and its vessels, and the recurrent laryngeal and pneumogastric nerves. It carries air from the larynx to the bronchi.

Trapezium
The trapezium is a small bone in the human hand below the little finger.

Trapezium bone
The trapezium bone is one of the bones in the human wrist.

Trapezius
The trapezius is a human muscle. It is a flat, triangular muscle, covering the back of the neck and shoulder.

Trapezoid bone
The trapezoid bone is one of the bones in the human wrist.

Triceps
The Triceps are muscles situated on the back of the upper arms in the human body.

Triquetral bone
The triquetral bone is one of the bones in the human wrist.

Trochanter
The trochanter is a protuberance in the upper part of the femur to which the muscles attach.

Trochoides
In anatomy, a trochoides is a pivot joint.

Trypsin
Trypsin is an enzyme present in pancreatic juice. It converts proteins into peptones.

Tympanum
The tympanum (middle ear) is a cavity in the temporal bone filled with air, closed externally by the tympanic membrane and containing a chain of small bones which convey sound vibrations to the inner ear.

Ulna
The ulnar is one of the two long bones which form the human lower arm. It connects with the humerus at the elbow.

Unciform
The unciform is a small bone in the human hand below the first finger.

Ureter
The Ureters are two membranous tubes which carry urine from the kidneys to the bladder in vertebrates.

Urethra
The urethra is a membranous canal which leads from the bladder to the outside world. It channels urine from the bladder out of the body.

Uterus
The uterus (womb) is the organ in which young are conceived, develop and are protected until birth.

Uvula
The uvula is a small conical prlongation from the middle of the soft palate.

Vein
A vein carries venous blood from the body to the heart.

Ventricle
The ventricles are chambers within the heart which force blood along the arteries.

Vertebra
The vertebrae are the bones of the vertebral column. Vertebrae are irregular bones comprised of two distinct parts, an anterior termed the body, and a posterior part termed the vertebral arch.

Vertebral column
The vertebral column (spinal column, spine) is the central axis of all vertebrate animals. It is comprised of a number of independent irregular bones (vertebrae), which are firmly connected to one another, but are capable of a limited amount of independent movement.

Vomer
The vomer is a thin flat bone which forms the hinder and lower part of the septum of the human nose.

Waist
The waist is the part of the body between the ribs and the hips.

Wharton's Duct
Wharton's duct is the duct leading from the submaxillary gland into the mouth, and opening under the tongue through a papilla at the side of the fold of membrane that joins the tongue to the floor of the mouth.

Womb
see "Uterus"

Yolk
The yolk is part of an embryo which serves as nutrition for the rest of the embryo.

Zygomatic bone
In a human, the zygomatic bone is the bone in the skull responsible for the prominence of the upper and anterior part of the cheek. It forms the lateral part of the lower margin of the orbital opening.

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