Protovertebrae

The primitive segments of the mesoblast in the site of the future verlebral column.

Protozoa

That division of the protista which has been assigned to the animal kingdom.

Proximal

A term used to denote a part relatively nearer to the centre.

Pseudopodia

Projections thrown out by moving protoplasm, by means of which cells, such as amoebae, move.

Ptosis

Drooping of the eyelid accompanying paralysis of the third nerve.

Ptyalin

The ferment of the saliva. In a weak alkaline solution it converts starch into dextrine and sugar.

Reflex Action

The activity caused by a ganglion cell reflecting an afferent impulse along an efferent nerve to the neighborhood of original stimiflation.

Reflexion

The return of rays of light from a surface.

Refraction

The bending which rays of light undergo when passing obliquely from one medium to another of different density.

Reticulum

A network; a term applied to the interlacement of fibres, seen in reticulated connective tissue, etc.

Rheoscopic Frog

An arrangement by which the change in the electric current of one muscle of a frog: is made to act as a stimulus to the nerve of another.

Saponification

The formation of soap; the decomposition of oils or fats by means of alkalies into salts of the fatty acids and glycerine.

Sarcolactic Acid

The principal acid in dead muscle. It has a dextro-rotatory power on polarized light, which ordinary lactic acid does not possess.

Sarcolemma

The delicate sheath surrounding the fibres of skeletal muscles.

Sclerotic

The fibrous coat of the eyeball.

Sensorium

That part of the nerve centres supposed to receive sensory impressions.

Somatopleure

The subdivision of the mesoblast which, with the attached epiblast, forms the body walls of the embryo.

Specific Gravity

The relation of the weight of a given volume of any substance to the weight of an equal volume of distilled water at 40 C.

Spherical Aberration

An indistinctness of the image caused by the difference in refraction at the centre and margin of a lens giving rise to different focal lengths.

Sphygmograph

An instrument for obtaining a graphic representation of the pulse wave by means of a lever applied to the radial artery at the wrist.

Splanchnopleure

The subdivision of the mesoblast which, with the attached hypoblast, forms the chief visceral cavities of the embryo.

Sporadic Ganglia

Swellings occurring in the course of the peripheral nerves caused by a group of nerve corpuscles.

Steapsin

A ferment existing in the pancreatic juice which causes or aids the saponification of the fats.

Sudoriferous Glands

The small tubular glands of the skin which secrete perspiration.

Summation

The fusion of several single contractions of muscle to form a tetanic contraction; the accumulation of stimuli.

Sutures

Unions formed by the direct apposition of bones without intervening cartilage. They do not permit of motion.

Sympathetic Nerve

The ganglionic nervous cord on either side of the vertebral column. It transmits most of the vasomotor impulses coming from the cerebro-spinal centres.

Symphysis

A form of joint without synovial membrane in which the bones are fixed together by fibro-cartilage.

Synthesis

The artificial construction of a chemical compound from simpler materials.

Systole

The period of contraction of the heart's muscle.

Taurocholic Acid

An acid existing in combination with soda in the bile.

Tetanus

In physiology is used to denote the prolonged contraction of the skeletal muscles which follows rapidly repeated stimulations or nervous impulse.

Thalamencephalon

That part of the anterior cerebral vesicle which is left after the differentiation of the optic thalami, cerebral hemispheres, etc.

Thrombosis

The occlusion of a vessel by a local coagulation of the blood.

Trabecular

Supporting bars of tissue passing through some organs, such as those proceeding from the capsule to the interior of the spleen or lymphatic glands.

Trophic

Relating to nutrition.

Trypsin

A ferment in the pancreatic juice which in alkaline solutions converts proteids into peptones.

Tyrosin

A substance formed together with leucin during pancreatic digestion; it is also produced by putrefaction of proteids.

Urachus

The bond of union which at an early period connects the urinary bladder with the allantois in the embryo; it is subsequently obliterated in the foetus.

Vacuoles

Small cavities occurring in cells. They are supposed to have im portant functions in the unicellular organisms.

Vagus

The part of the eighth pair of nerves distributed to the viscera of the throat, thorax and abdomen; the great regulating nerve of the vegetative functions.

Vaso-Constrictor

Those impulses which excite contraction of the vascular muscles.

Vaso-Dilator

Those impulses which inhibit the action of the vascular muscles.

Vasomotor

Those nervous mechanisms controlling the movements of the blood vessels.

Villus

A hair-like process. A term applied to the small projections characteristic of the small intestine. They contain blood vessels and lacteals, and are important in absorption.

Vitellus

The yolk of the ovum, which in mammals divides completely to form the embryo. In birds only a part divides, and the rest serves to nourish the chick.

Vorticella

Bell animalcule, a bell-shaped unicellular organism with a rudimentary, ciliated mouth cavity and rapidly contractile stalk.

Wolffian Body

An embryonic structure, the forerunner of certain parts of the genito-urinary apparatus.

Zymogen

A peculiar substance supposed to give rise to the pancreatic ferments.