exteriorly by the urethra. It is attached to the abdominal walls by a rounded cord, the urachus, the remains of a portion of the allantois.

Genito- Urinary Apparatus. The Wolffian bodies appear about the thirtieth day, as long hollow tubes running along each side of the primitive vertebral column. They are temporary structures, and are sometimes called the primordial kidneys. The Wolffian bodies consist of tubules which run transversely and are lined with epithelium; internally they become invaginated to receive tufts of blood vessels; externally they open into a common excretory duct, the duct of the Wolffian body, which unites with the duct of the opposite body, and empties into the intestinal canal at a point opposite the allantois. On the outer side of the Wolffian body there appears another duct, the duct of Müller, which also opens into the intestine.

Behind the Wolffian bodies are developed the structures which become either the ovaries or testicles. In the development of the female, the Wolffian bodies and their ducts disappear; the extremities of the Müllerian ducts dilate and form the fimbriated extremity of the Fallopian tubes, while the lower portions coalesce to form the body of the uterus and vagina, which now separate themselves from the intestine.

In the development of the male, the Müllerian ducts atrophy, and the ducts of the Wolffian body ultimately form the epididymis and vas deferens. About the seventh month the testicles begin to descend, and by the ninth month have passed through the abdominal ring into the scrotum.

The Kidneys are developed out of the Wolffian bodies. They consist of little pyramidal lobules, composed of tubules which open at the apex into the pelvis. As they pass outward they become convoluted and cup-shaped at their extremities, receive a tuft of blood vessels, and form the Malpighian bodies.

The ureters are developed from the kidneys, and pass downward to be connected with the bladder.

The Circulatory Apparatus assumes three different forms at different periods of life, all having reference to the manner in which the embryo receives nutritious matter and is freed of waste products.

The Vitelline circulation appears first and absorbs nutritious material from the vitellus. It is formed by blood vessels which emerge from the body and ramify over a portion of the vitelline membrane, constituting the area vasculosa. The heart, lying in the median line, gives off two arches which unite to form the abdominal aorta, from which two large arteries are given off, passing into the vascular area; the venous blood is returned

by veins which enter the heart. mesenteric arteries and veins.

These vessels are known as the omphaloThe vitelline circulation is of short duration in the mammals, as the supply of nutritious matter in the vitellus soon becomes exhausted.

The Placental circulation becomes established when the blood vessels in the allantois enter the villous processes of the chorion and come into close relationship with the maternal blood vessels. This circulation lasts during the whole of intra-uterine life, but gives way at birth to the adult circulation, the change being made possible by the development of the circulatory apparatus.

The Heart appears as a mass of cells coming off from the anterior portion of the intestine; its central part liquefies, and pulsations soon begin. The heart is at first tubular, receiving posteriorly the venous trunks and giving off anteriorly the arterial trunks. It soon becomes twisted upon itself, so that the two extremities lie upon the same plane.

The heart now consists of a single auricle and a single ventricle. A septum growing from the apex of the ventricle divides it into two cavities, a right and a left. The auricles also become partly separated by a septum which is perforated by the foramen ovale. The arterial trunk becomes separated by a partition, into two canals, which become, ultimately, the aorta and pulmonary artery. The auricles are separated from the ventricles by incomplete septa, through which the blood passes into the ventricles. Arteries. The aorta arises from the cephalic extremity of the heart and divides into two branches which ascend, one on each side of the intestine, and unite posteriorly to form the main aorta; posteriorly to these first aortic arches four others are developed, so that there are five altogether running along the visceral arches. The two anterior soon disappear. The third arch becomes the internal carotid and the external carotid; a part of the fourth arch, on the right side, becomes the subclavian artery, and the remainder atrophies and disappears, but on the left side it enlarges and becomes the permanent aorta; the fifth arch becomes the pulmonary artery on the left side. The communication between the pulmonary artery and the aorta, the ductus arteriosus, disappears at an early period.

Veins. The venous system appears first as two short, transverse veins, the canals of Cuvier, formed by the union of the vertebral veins and the cardinal veins, which empty into the auricle. The inferior vena cava is formed as the kidneys develop, by the union of the renal veins, which, in a short time, receive branches from the lower extremities. The subclavian veins join the jugular as the upper extremities develop. The heart descends in the thorax, and the canals of Cuvier become oblique; they

shortly communicate by a transverse duct, which ultimately becomes the left innominate vein. The left canal of Cuvier atrophies and becomes a fibrous cord. A transverse branch now appears, which carries the blood from the left cardinal vein into the right, and becomes the vena azygos minor; the right cardinal vein becomes the vena azygos major.

Circulation of Blood in the Foetus. The blood returning from the placenta, after having received oxygen, and being freed from carbonic acid, is carried by the umbilical vein to the under surface of the liver; here a portion of it passes through the ductus venosus into the ascending vena cava, while the remainder flows through the liver, and passes into the vena cava by the hepatic veins. When the blood is emptied into the right auricle, it is directed by the Eustachian valve, through the foramen ovale, into the left auricle, thence into the left ventricle, and so into the aorta to all parts of the system. The venous blood returning from the head and upper extremities is emptied, by the superior vena cava, into the right auricle, from which it passes into the right ventricle, and thence into the pulmonary artery. Owing to the condition of the lung, only a small portion flows through the pulmonary capillaries, the greater part passing through the ductus arteriosus, which opens into the aorta at a point below the origin of the carotid and subclavian arteries. The mixed blood now passes down the aorta to supply the lower extremities, but a portion of it is directed, by the hypogastric arteries, to the placenta, to be again oxygenated.

At birth, the placental circulation gives way to the circulation of the adult. As soon as the child begins to breathe, the lungs expand, blood flows freely through the pulmonary capillaries, and the ductus arteriosus begins to contract. The foramen ovale closes about the tenth day. The unbilical vein, the ductus venosus, and the hypogastric arteries become impervious in several days, and ultimately form rounded cords.

TABLE OF PHYSIOLOGICAL CONSTANTS.

Mean height of male, 5 feet 61⁄2 inches; of female, 5 feet 2 inches.
Mean weight of male, 145 pounds; of female, 121 pounds.
Number of chemical elements in the human body; from 16 to 18.
Number of proximate principles in the human body; about 100.
Amount of water in the body weighing 145 pounds; 108 pounds.
Amount of solids in the body weighing 145 pounds; 36 pounds.
Amount of food required daily; 16 ounces meat, 19 ounces of bread, 31⁄2

ounces of fat, 52 ounces of water.

Amount of saliva secreted in 24 hours; about 31⁄2 pounds.

Function of saliva; converts starch into glucose.

Active principle of saliva; ptyalin.

Amount of gastric juice secreted in 24 hours; from 8 to 14 pounds.
Functions of gastric juice; converts albumen into albuminose.

Active principles of gastric juice; pepsin and hydrochloric acid. Duration of digestion; from 3 to 5 hours.

Amount of intestinal juice secreted in 24 hours; about I pound.

I

Function of intestinal juice; converts starch into glucose. Amount of pancreatic juice secreted in 24 hours; about 11⁄2 pounds. Active principles of pancreatic juice; pancreatin and trypsin.

Functions:

{

1. Emulsifies fats.

2. Converts albumen into albuminose.

3. Converts starch into glucose.

Amount of bile poured into the intestines daily; about 21⁄2 pounds.

Functions:

1. Assists in the emulsification of fats.

2. Stimulates the peristaltic movements.

3. Prevents putrefactive changes in the food.
4. Promotes the absorption of the fat.

Amount of blood in the body; from 16 to 18 pounds.

Size of red corpuscles; 32 of an inch.

Size of white corpuscles; of an inch.

Shape of red corpuscles; circular biconcave disks.

Shape of white corpuscles; globular.

Number of red corpuscles in a cubic millimetre of blood (the cubic

of an inch); 5,000,000.

Function of red corpuscles; to carry oxygen from the lungs to the tissues. Frequency of the heart's pulsations per minute; 72, on the average. Velocity of the blood movement in the arteries; about 16 inches per second.

Length of time required for the blood to make an entire circuit of the vascular system; about 20 seconds.

Amount of air passing in and out of the lungs at each respiratory act; from 20 to 30 cubic inches.

Amount of air that can be taken into the lungs on a forced inspiration; IIO cubic inches.

Amount of reserve air in the lungs after an ordinary expiration; 100 cubic inches.

Amount of residual air always remaining in the lungs; about 100 cubic inches.

Vital capacity of the lungs; 230 cubic inches.

Entire volume of air passing in and out of the lungs in 24 hours; about 400 cubic feet.

Composition of the air; nitrogen, 79.19, oxygen, 20.81, per 100 parts. Amount of oxygen absorbed in 24 hours; 18 cubic feet.

Amount of carbonic acid exhaled in 24 hours; 14 cubic feet.

Temperature of the human body at the surface; 98° F.

Amount of urine excreted daily; from 40 to 50 ounces.

Amount of urea excreted daily; 512 grains.

Specific gravity of urine; from 1.010 to 1.015.

Number of spinal nerves; 31 pairs.

Number of roots of origin; two; Ist, anterior, motor; 2d, posterior,

sensory.

Rate of transmission of nerve force; about 100 feet per second.

Number of cranial nerves; 12 pairs.

Nerves of special sense:

Motor nerves to eyeball and

1. Olfactory, or 1st pair.
2. Optic, or 2d pair.

3. Auditory, or 8th pair.

4. Chorda tympani for anterior 2/3 of tongue. 5. Branches of glosso-pharyngeal, or 8th pair, for posterior of tongue.

accessory structures; motor oculi, or 3d pair; pathetic, or 4th pair; abducens, or 6th pair. Motor nerves to facial muscles; portio dura, facial, or 7th pair. Motor nerve to tongue; hypoglossal or 12th pair.

Motor nerve to laryngeal muscles; spinal accessory or 11th pair.