THE FRAMEWORK OF THE BODY
The framework of the body undergoes a gradual development from birth to maturity. It represents the bony structure of the body; and on it all other parts depend for support and protection. The brief summary of its parts and work that follows here has been adapted from Wilcox and Smith.
The Skeleton.
—This consists of a backbone, skull, shoulder girdle, pelvic girdle, and two pairs of appendages. The backbone may be conveniently divided into regions, each comprising a certain number of vertebræ. The cervical vertebræ include those from the skull from the first rib. In all mammals except the sloth and sea cow the number of cervical vertebræ is seven, being long or short, according as the neck of the animal is relatively long or short. The first and second cervical vertebræ, known as the atlas and axis, are especially modified so as to allow free turning movements of the head.
The next region includes the dorsal or thoracic vertebræ, which are characterized by having ribs movably articulated with them. The number is 13 in the cat, dog, ox, sheep, and goat; 14 in the hog; 18 or 19 in the horse and ass, and six or seven in domestic poultry. In mammals they are so joined together as to permit motion in several directions, but in poultry the dorsal vertebræ are more rigidly articulated, those next to the sacrum often being grown together with the sacrum. The spines are high and much flattened in all ungulates, long and slender in dogs and cats. They slope backward, forming strong points of attachment for the back muscles. Several ribs, varying in number in different animals, meet and become articulated with the breast bone or sternum. The sternum consists of seven to nine articulated segments in our domestic mammals, while in fowls the sternum is one thin high bone furnished with a keel of varying depth. The lumbar vertebræ lie between the dorsal vertebræ and the sacrum. The number is five in the horse, six in the hog, ox and goat, and seven in the sheep. The sacrum is made up of a certain number of vertebræ, which are rigidly united and serve as an articulation for the pelvic arch. The number of sacral vertebræ is five in the ox and horse, four in sheep and hogs, and 12 to 17 in birds. The caudal or tail vertebræ naturally vary in number according to the length of the tail (7 to 10 in sheep, 21 in the ox, 23 in hogs, 17 in the horse, 22 in the cat, 16 to 23 in the dog).
In ungulates the anterior ribs are scarcely curved, the chest being very narrow in front. The number of pairs of ribs is the same as the number of dorsal vertebræ with which they articulate.
The Skull.
—This part of the skeleton is really composed of a number of modified vertebræ, just how many is not determined. The difference in the shape of the skulls of different animals is determined by the relative size of the various bones of the skull. In hogs, for example, the head has been much shortened as a result of breeding, thus giving the skull of the improved breeds a very different appearance from that of the razorback.
The shoulder girdle consists of a shoulder blade, collar bone and coracoid on either side. The fore leg (or wing, in case of birds) articulates with the socket formed by the junction of these three bones. In all the ungulates the shoulder blade is high and narrow, the coracoid is never much developed, and the collar bone is absent. In fowls all three bones of the shoulder girdle are well developed, the collar bone being represented by the “wish bone.”
The Pelvic Girdle.
—This consists of three bones on either side, viz., ilium, ischium, and pubis. The first two are directly articulated to the spinal column, while the pubic bones of either side unite below to complete the arch. The three bones of each side of the pelvis are present in all our domestic animals, including the fowls.
BONES OF THE SKELETON OF A HORSE
1 Face Bones, 2 Neck Bones or Cervical Vertebræ, 3 Scapula or Shoulder Blade, 4 Humerus or Arm Bone, 5 Radius or Bone of Forearm, 6 Carpus or Knee, 7 Shank Bone or Cannon, 8 Upper Pastern, 9 Lower Pastern, 10 Coffin Bone, 11 Ulna or Elbow, 12 Cartilages of the Rib, 13 Costæ or Ribs, 14 Dorsal Vertebræ or Bones of Back, 15 Lumbar Vertebræ or Bones of Loin, 16 Candal Vertebræ or Bones of Tail, 17 Haunch, 18 Femur or Thigh Bone, 19 Stifle Joint, 20 Tibia, 21 Tarsus or Hock, 22 Metatarsal Bones, 23 Upper Pastern Bone, 24 Lower Pastern Bone, 25 Coffin Bone.
Legbones of Farm Animals.
—There is one formula for the bones of the fore and hind legs of farm animals. The first segment is a single bone, the humerus of the fore leg, femur of the hind leg. In the next segment there are two bones, radius and ulna in the fore leg, tibia and fibula in the hind leg. In the dog, cat, and Belgian hare the radius and ulna are both well developed and distinct. In ungulates the humerus is short and stout, while the ulna is complete in the pig, rudimentary and behind the radius in ruminants and firmly united with the radius in the horse. Similarly with the hind leg the fibula is a complete bone in the pig, while in the horse there is merely a rudiment of it, attached to the tibia.
Feet.
—The mammalian skeleton has undergone the greatest modification in the bones of the feet. In the horse there are only six of the original ten wrist or carpal bones, and, since there is but one of the original five toes, the horse has also but one metacarpal or cannon bone. Splint-like rudiments of two other metacarpal bones are to be found at the upper end of the cannon bone, or at the “knee” joint. Below the cannon bone, and forming the shaft of the foot, we have the small cannon bone, coronary bone, and coffin bone—the last being within the hoof with the navicular bone behind it. The stifle joint of the horse corresponds to the knee of man. The “knee” of the horse’s fore leg corresponds to the hock of the hind leg, both being at the upper end of the cannon bone. The fetlock joint is between the large and small cannon bones, the pastern joint between the small cannon or large pastern bones, and the coffin joint between the coronary and coffin bones. The horse walks upon what corresponds to the nail of the middle finger and middle toe of man.
In pigs four digits touch the ground, the first being absent and the third and fourth larger and in front of the second and fifth. In ruminants the third and fourth digits reach the ground, while the second and fifth do not. In dogs the first digit appears on the side of the leg, not in contact with the ground.
ONE OF THE PARASITES OF THE HOG
The thorn-headed worm attached to the anterior part of the small intestine often causes death. Not more than five or six are usually found in a single animal.
In fowls the wing, which corresponds to the fore leg of mammals, shows a well-developed humerus, radius and ulna, while only one carpal and one metacarpal bone remain, along which the wing feathers are attached. In the leg the femur and tibia are strong bones, but the fibula is a mere splint. The tarsal bones are absent, while the shank consists of a metatarsal bone (really three bones fused together), to which the four toes are articulated.
The Muscular System of Farm Animals.
—The muscular system is too elaborate, the number of muscles too great, and their modifications for different purposes too complex for consideration in detail in the present volume. All muscles are either striped or unstriped (as examined under the microscope), according as they are under the immediate control of the will or not. The heart muscle forms an exception, for it is striped though involuntary. The essential characteristic of muscle fibers is contractility, which they possess in high degree. The typical striped muscles are concerned in locomotion, being attached at either end to a bone and extending across some movable joint. The most important unstriped muscles are found in the walls of the intestines and blood vessels.
The Nervous System.
—In so far as our present purposes are concerned, the nervous system may be disposed of in a few words. The central nervous system consists of a brain and spinal cord. The microscopic elements of this tissue are peculiarly modified cells, consisting of a central body, from which fibers run in two or more directions. The cell bodies constitute the gray matter, and the fibers the white matter of the brain and spinal cord. The gray substance is inside the spinal cord and on the surface of the brain, constituting the cortex. The most important parts of the brain are the cerebrum, optic lobes, cerebellum, and medulla. There are twelve pairs of cranial nerves originating in the brain and controlling the special senses, movements of the face, respiration, and pulse rate. From each segment of the spinal cord a pair of spinal nerves arises, each of which possess both sensory and motor roots. The sympathetic nervous system consists of a trunk on either side, running from the base of the skull to the pelvis, furnished with ganglionic enlargements and connected with the spinal nerves by small fibers.
The Respiratory Organs.
—These include the nose, larynx, trachea or windpipe, and lungs. The trachea forks into bronchi and bronchioles of smaller and smaller size, ending in the alveoli or blind sacs of the lungs. In fowls there are numerous extensions of the respiratory system known as air sacs, and located in the body cavity and also in the hollow bones. The air sacs communicate with the lungs, but not with one another.
The Urinary Organs.
—These consist of kidneys connecting by means of ureters with a bladder from which the urethra conducts the urine to the outside. In the male the urethra passes through the penis and in the female it ends just above the opening of the vagina. The kidneys are usually inclosed in a capsule of fat. The right kidney of the horse is heart-shaped, the left bean-shaped. Each kidney of the ox shows 15 to 20 lobes, and is oval in form. The kidneys of sheep, goats, and swine are bean-shaped and without lobes.
The Reproductive Apparatus.
—This consists of ovaries, oviducts, uterus or womb, and vagina in the female; the testes, spermatic cords, seminal vesicle and penis, together with various connecting glands, especially prostate gland and Cowper’s gland, in the male. In fowls there is no urinary bladder, but the ureters open into the cloaca or posterior part of the rectum. The vagina and uterus are also wanting in fowls, the oviducts opening directly into the rectum. The male copulating organ is absent except in ducks, geese, swan, and the ostrich.
CHAPTER II
Some Physiology You Ought to Know
A close relation exists between the soil, plant, and the animal. One really cannot exist without the other to fulfill its destiny. A soil without plant or animal growth is barren, devoid of life. The soil comes first; the elements contained in it and the air are the basis of plant and animal life. The body of the animal is made up of the identical elements found in the plant, yet the growth of the plant is necessary to furnish food for animal life. The plant takes from the soil and from the air the simple chemical elements, and with these builds up the plant tissue which, in its turn, is the food of the animal.
The animal cannot feed directly from the soil and air; it requires the plant first to take the elements and to build them into tissue. From this tissue animals get their food for maintenance and growth. Then the animal dies; with its decay and decomposition comes change of animal tissue, back to soil and air again; back to single simple elements, that new plants may be grown, that new plant tissue may be made for another generation of animal life.
Thus the plant grows out of the soil and air, and the decay of the animal plant life furnishes food for the plant that the plant may furnish food for the animal. Thus we see the cycle of life; from the soil and air come the soil constituents.
CIRCULATION AND DIGESTION
1 Mouth, 2 Pharynx, 3 Trachea, 4 Jugular Vein, 5 Carotid Artery, 6 Œsophagus, 7 Posterior Aorta, 8 Lungs, 9 External Thoracic Artery, 10 Left Auricle, 11 Right Auricle, 12 Diaphragm, 13 Spleen, 14 Stomach, 15 Duodenum, 16 Liver, upper extremity, 17 Large Colon, 18 Left Kidney and its Ureter, 19 Floating Colon, 20 Rectum, 21 Anus, 22 Bladder, 23 Urethra, 24 Small Intestine, 25 Cæcum, 26 Venous Supply to the Foot, 27 Posterior Tibial Artery, 28 Internal Metatarsal Vein, 29 Internal Metatcarpal Vein, 30 Posterior Radial Artery, 31 Metacarpal Artery, 32 Vertebral Artery, 33 Superior Cervical Artery, 34 Anterior Dorsal Artery.