Notes on Veterinary Anatomy

by Charles James Korinek

GENERATIVE SYSTEM OF THE HORSE.

Animals possess the faculty of reproducing or propagating their species, and this function may be non-sexual or sexual, the former being confined to certain lowly-organized classes of animals.

In all the higher animals the generation of a new being is dependent upon two individuals, a male and a female, the female furnishing a germ, or ovum, the male a fecundating fluid, or sperm, which animates the germ and renders it fit for development.

Both the ovum of the female and the sperm of the male are secretions of glands, which are termed the genital glands, male and female; and in either sex the generative system may be said to consist of these glands, with certain accessory organs. The act of coition brings the two secretions into contact.

We have two systems of genital organs to consider—the male and the female.

Male.—The genital organs of the horse are as follows: The scrotum or bag, the testicles, the spermatic cord, the vesiculae seminales or pouches which hold the semen or sperm, the urethra, the penis and the sheath.

The Scrotum is a sac or bag which contains the testicles. It is situated between the hind legs, and is covered on the outside by a very fine, soft skin. Passing up in the center under the sheath the scrotum is a well marked line in the skin called median raphe. This can be plainly seen when the horse is on his back. It continues up, gradually getting fainter until it reaches the anus. Under the skin are layers of white fascia or tissue which can be seen by cutting through the scrotum. There is a partition in the scrotum separating the two testicles. The size of the scrotum is affected very much by the weather. In cold weather its fibres contract, causing it to get very much smaller, while in warm weather the fibres relax, causing it to become very much larger. The scrotum contains, supports and protects the testicles.

The Testicles are the glands which secrete the semen or sperm. They are two in number, one situated on the left side and the other on the right. They are oval in shape, and are attached above to the spermatic cord. Before the animal is born the testicles are situated in the abdominal cavity and attached to the serous membrane which has already been spoken of in connection with that cavity. At or about the time of birth, there takes place what is known as the descent of the testicles into the scrotum. In their downward course they pass through a slit or small opening at the back part of the muscles of the abdomen, where they are attached to the under part of the hip bone. These slits or openings are known as the inguinal rings. They can be felt in the horse by pressing the fingers well up into the groins. The descent of the testicles is an important point to remember. If the testicle does not descend into the scrotum the horse is known as a ridgling. In this case the testicle is not found in the scrotum. At the front part of the testicle there is a small ridge called the globus major and at the back of it is another smaller ridge called the globus minor. Passing between these two ridges is another well marked ridge called the epididymis. These can be easily seen by examining the testicle after the animal is altered or castrated. The substance of the testicle is made up of small glands and fine tubes.

These tubes, as they pass towards the back of the testicle, form into larger tubes and finally unite to form one called the vas deferens.

The Spermatic Cords, or the cords of the testicles, are attached above to the inguinal rings or openings mentioned before. They are about five or six inches long and have the testicles attached to them below. In each cord is found a small muscle which goes by the name of the spermatic muscle, the rest of the cord being made up of the spermatic artery, veins and nerves. Running up at the back of these cords is found a tube called the vas deferens. Around the spermatic cords and testicles is a serous membrane, one layer being attached to the testicle and cord, while the other is closely attached around the inside of the scrotum. In this membrane are small glands which secrete an oily fluid to lubricate the parts, preventing friction when they are jolted about in the scrotum. This fluid flies out as soon as the scrotum is cut. This is important, because sometimes from a slight injury the glands will secrete a large amount of this fluid, thus causing the scrotum to look large and swollen. This disease is known as hydrocele or water in the scrotum.

Vas Deferens.—These tubes are two in number and are situated just behind the spermatic cords. They are about an eighth of an inch in diameter and quite hard. They carry the semen up the back part of the spermatic cord through the inguinal rings, before mentioned. They pass backward and upwards, one on each side, to the upper part of the bladder, where they empty into two small pouches or sacs, called the vesiculae seminales. These store up the semen as it is secreted by the testicles, and when full present the appearance of a pear.

Vesiculae Seminales.—These sacs or pouches are situated at the upper side, over the neck of the bladder, one on each side. They have the vas deferens emptying into them at the front end, while at the back end of each is a small opening that leads out into another small tube which passes backward and empties into the urethra, mentioned before as carrying the urine out from the bladder. These sacs or pouches store up the semen or sperm of the horse. During sexual intercourse, these pouches contract and force the semen through the little tubes mentioned out into the urethra, leading down through the penis.

The Penis is the main organ of sexual intercourse. Its substance is formed of what is known as erectile tissue, which under certain circumstances becomes enormously distended with blood. Passing up the under side there is, what has already been mentioned, the urethra, or the tube, which carries the urine out of the body, and also in the act of intercourse carries the semen. This is used for two purposes, as we have already mentioned.

The Sheath is a loose process of skin which passes downward from the scrotum, generally from about five to six inches, according to the size of the animal. It is attached to each side, leaving a hole or opening in the center through which the penis passes. The outside of the sheath is covered by a thin, delicate skin similar to that of the scrotum. It is lined inside by a membrane containing many small glands, which secrete a thick, dark fluid to lubricate this passage. Sometimes this fluid collects in here and has the appearance of tar. This is important, for when it collects to a large extent the sheath should be washed.

The Semen or sperm of the horse is a light fluid, which, when examined under a microscope is found to contain small objects called spermatozoa. These move about, and when in the womb meet the ovum of the female, which is secreted by a gland called the ovary. When these two small objects unite, they form the foetus, or what may be called the animal in its first stage of development.