The nostrils are narrow and capable of little dilation compared to those of the horse. The nasal chambers differ chiefly in there being an additional turbinated bone. The nasal chambers communicate with the mouth, therefore cattle can breathe through the mouth to a certain extent. The larynx is simpler in construction, the true vocal cords being only slightly developed. The trachea or windpipe presents no important variation. We may note the presence of a third bronchus, which passes to the right lung to supply a lobe which is wanting in the horse.
The Thoracic Cavity is relatively smaller in the ruminants, and the pleurae present a very important deviation from the arrangement found in the solipede—viz., the back or posterior mediastinum is imperforate and strong, completely separating one pleural sac from the other. This arrangement exists in all the domesticated mammals but the solipede. The left lung is divided into two lobes, the right into four, the front one recurving over and almost covering the front of the heart. The interlobular or cellular tissue is exceedingly thick, the separation between the lobules being distinctly visible. This arrangement explains perfectly the special nature of pneumonic lesions in the large ruminants.
URINARY SYSTEM OF THE HORSE.
The organs of this system secrete the urine from the blood, and excrete or expel it from the body. These organs are chiefly the kidneys, ureters, bladder and urethra. The urine, which is a watery fluid, is secreted by the kidneys, and carried off by their ducts, the ureters, to a special reservoir, the bladder, where it accumulates and from which it is finally expelled at intervals through the urethra.
The kidneys are two compound tubular glands, one on the right side and one on the left side, and are situated just below the small of the back (sublumbar region), the right one being the fartherest ahead. In shape they are long and narrow and resemble the liver in color. In cutting one of the kidneys open, it is found to be full of glands and tubes, which secrete the urine from the blood while it is passing through the kidneys. These tubes pass to the center of the kidneys, where they empty the urine into what is called the pelvis. The glands are largely supplied with blood vessels and nerves. The use of the kidneys are to secrete the urine from the blood, which contains a large amount of what is known as ureaic acid, and if not taken out of the blood by these glands, acts as a poison to the system.
The Ureters are tubes which carry the urine down from the pelvis of the kidney to the bladder. They are two in number, one situated on the right side of the pelvic cavity and the other on the left side, close to the walls—they enter on each side at the upper surface of the bladder. They are only about one-sixteenth of an inch in diameter.
The Bladder is situated in the pelvic cavity. When it is full it sometimes stretches out into the abdominal cavity. It consists of a body and neck. The body is the large part, and is placed in front; the neck being at the back part of the bladder. This is where the urine passes out of the bladder. The bladder is made up of three coats, somewhat similar to that of the bowels. The serous coat is a continuation of the serous coat found in the abdominal cavity lining the bowels. The inside is lined with mucous membrane which is thrown into folds when the bladder is empty. Another coat is found between the two membranes above mentioned, called the muscular coat, the action of which is to contract the bladder when the animal wants to urinate. The bladder is held in by ligaments. The rectum lies above the bladder, which in the horse rests on the floor of the pelvic cavity. Its position in the mare differs from that of the horse. Instead of the rectum or back bowel being immediately above it, as in the horse, the womb is just above the bladder or between it and the rectum. The bladder acts as a reservoir in which to store the urine until it is full; it then presses on the walls and nerves, giving a peculiar sensation to these parts, causing the walls to contract, forcing the urine into a tube which carries it from the body. This is called the urethra. The neck of the bladder is simply an opening at the back part, and is guarded by a valve which prevents the urine from dripping out except when the animal is passing its urine or water.
The Urethra is the tube which carries the urine from the bladder out of the body. It is situated much differently in the mare than in the horse. In the mare it is very short, passing from the neck of the bladder along below the womb and vagina, which is the passage from the outside into the neck of the womb. It opens up into the underside of this passage about four inches in from the outside. This opening is guarded by a small, thin valve, and can be felt by passing the finger along the under side of the passage which leads into the womb. In the horse this tube is a great deal longer than in the mare. It commences at the bladder, passes along below the rectum or back bowel to just below the anus. Here this tube bends downward and forward and passes into the penis, continuing down to the end where it terminates. Its purpose is to carry the urine from the bladder out of the body and to perform certain actions in connection with the genital organs. Its lining is a continuation of the membrane of the bladder.