Book VII. PHYSIOLOGY OF THE HORSE, 907 



SuBSECT. 14. The Organs of Generation. 



5739. The male generative ofgans are most of them external, on the contrary in 

 man they are mostly internal ; but in both the one and the other they are connected with 

 the urinary organs, so that one general formation is made to answer a double purpose. 



5740. The male organs of generation consist of the testes or testicles, which are two in number, that 

 in case one should suffer injury, one may remain to carry on the great work of reproduction. In the 

 fcetal colt they are lodged within the belly, but after birth they descend into a bag prepared for them. The 

 scrotum is this hag, whose situation is between the hinder extremities. It contains the testicles in two 

 sacs, one appropriate to each. Each testicle is enveloped by two tunics, called vaginalis and albuginea, 

 obtained from the peritoneum. To each testicle is attached an appendage called the epididymis. The 

 vasa deferentia are the united trunks of the secretory vessels of the testicle continued from the epididy- 

 mis. Each vas deferens proceeds to join the vcsicula seminales of that side to run parallel with it 

 and to terminate near it in the urethra. The prostate glands are in the horse two, whose uscylike the 

 hollow bodies called seminal receptacles, is not obvious, but probably they dilute the semen. 



5741. The penis or yard is a long body, in one part nearly prismatic, and in another cylindrical. In the 

 usual state the penis is hidden within the sheath, which is a prolongation of the skin of the abdomen. 

 The body of the yard is composed of two cavernous flattened portions closely connected, a spongy canal, 

 which is the urethra before mentioned as the continuation of the bladder, and the glans or head, which 

 appears in the horse a distinct part. The penis is/capable of being distended by means of its blood vessels, 

 which fill its cells to turgidity, particularly under the excitement of lust. 



5742. The generating use of the male organs is principally derived from the vivifying principle con- 

 tained in the semen secreted within the testicles, and which the horse is impelled by lust to plant in such 

 a situation as shall produce its effect in the formation of a foetus. In the act of copulation therefore, itap- 

 pears that the nervous influence acts on the muscular system of the penis, whereby the arteries carry more 

 blood, while the veins are rendered unable from some cause to effect its removal ; by which the cavernous 

 cells of the penis become filled, and the member thereby erected ; when, from the friction produced by 

 the female vagina, the penis becomes stimulated into a more exquisite sensation, with which the vasa 

 deferentia and vesiculas seminales participate, then by the assistance of the crcmaster muscles, the 

 semen and diluting fluids become pressed out, and by a "convulsive effort are injected into the generative 

 organs of the mare. The stimulus of the retained semen being now removed, the appetite becomes sa- 

 tisfied, the nervous influence is removed from the vessels, and the penis returns to its ordinary size. 



5743. The female generative organs are flrst the bag or mammce. In the multiparous animals, as the 

 hog, the dog, and rabbit, these bags are numerous, and distinctly placed along the line of the abdomen j 

 but in the uniparous, as the mare, cow, sheep, &c., one bag, situated between the hind legs, contains the 

 secretary of the whole. In the mare there are two nipples or teats, Vvhich form excretory ducts to the milk 

 secreted within. In ordinary cases, the milk is prevented from flowing out by valves, which open on pres- 

 sure upwards : the colt, sensible of this, is observed to push up the teat with its nose ; pigs and puppies with 

 their feet, &c. The milk in different animals has different proportions of certain component parts, but in each 

 it has those best adapted to the animal it is intended to nourish. The volva or sheath is the long oval opening 

 immediately below the anus, at the inferior commissure of which is situated the clitoris, whose structure 

 is not unlike the male penis. Above this, and rather more internally, is situated the urethra, which in 

 the mare is a short membranous canal. The vagina is a long membranous canal above the last described 

 parts, capable of great distention; but in its natural state about 9 or IG inches long and 2^ in diameter. 

 It is placed horizontally between the bladder and rectum, and terminates in the neck of the womb. The 

 uterus (fig. 618 p) of the mare is very dissimilar to the human, being not an uniform bag ; but having a 

 body and two branching ho7-ns, in which, in the multiparous animals, the young are lodged. The extre- 

 mity of each cornua has a small concealed tube attached to it called the fallopian tube,&ndL a little beyond 

 are seen the oval oblong bodies called ovaria, {fig. 618 gg). 



5744. Conception, pregnancy, and evolution of the foetus. (Estrum, heat, or horsing is in animals not 

 constant, but returns at such periods that the evolution of the foetus consequent on it shall take place at 

 the most convenient season of the year. The horsing of the mare produces an inflammation in the va- 

 gina and vulva, from whence are ejected what are termed the heats. In this disposition all the parts 

 unite, and when by the injected semen pregnancy has been produced, a vesicle from the ovaria enters the 

 fallopian tubes ; and by this means becomes deposited in the womb to be nourished into maturity. In its 

 residence within the womb, it is covered with expansions from the neighboring parts ; and i! derives its 

 nourishment from a communication with the mother by a fleshy tube called the umbilical cord, and thus 

 situated, it swims within a fluid called the liquor amnii : so circumstanced, the foetus continues to grow, un- 

 til the distention it occasions, becomes too great for the capacity, when the muscular fibres of the uterus, 

 powerfully assisted by the diaphragm and abdominal muscles, contract, and thus force both the foal and 

 the membranes into the world. 



5745. The new born foal, on its entrance into active life, finds its organs of immediate necessity in a fulf 

 state of capacity. Unlike the infant, it is far from indigent, but can run and perform the common 

 phenomena of an animal with dexterity and ease. Its powers are however not sufficiently developed to 

 enable it to live independent : it has therefore a necessity for seeking support from the mother, from whose 

 person it derives its food in the form of milk ; and it may therefore be now considered in some measure as 

 carnivorous. Gradually it becomes fitted to perform all the more matured functions, and when fully able 

 to counteract its own wants, it sympathises only with itself; when the parent's care being no longer ne- 

 cessary, lactiferous secretion ceases, her generative organs prepare anew for the same great work, and 

 she again feels oestrum or heat. 



5746. The period of gestation varies in different mares, one hundred and two mares were observed by 

 Tessier, of which 3 foaled on the 311th day, 1 on the 314th, 1 on the 325th, 1 on the 326th, 2 on the 3.')3th 

 47 from the 340th to the S50th, 25 from the 350th to the 360th, 21 from the 360th to the 377th, and 1 on the 

 S94th day : which gives a latitude of 83 days in the time of gestation. 



SuBSECT. 15. The Foot. 



574'7 . The feet of the horse present in their united functions a series of springs with great 

 complexity of structure. An unreflecting observer considers only the horny box, and 

 perhaps attaches as little merit to its mechanism, as he would to a well turned 

 wooden leg of a man. But a little examination will convince him that all the complex- 

 ity, all the admirable mechanism displayed in the assemblage of four fingers and a 

 thumb, are here concentrated within this horny box and its appendages. As the parts 

 which compose the hind and the fore feet do not materially differ, a description of one 

 foot will serve for the whole. 



5748. On examining a perpendicular section of the foot and pastern {fig. 620.), there appears the cofBn- 

 bone (a), the navicular or nut bone {h), the coronary or little pastern bone (c), the larger pastern 



