SPLANCHNOLOGY.
Study of large interior organs in any of the four great bodily cavities
especially those in the abdomen.
DIGESTIVE ORGANS OF THE HORSE.--The digestive organs comprise the
alimentary canal and the accessories by which the alimentary matter is
received and subjected to specific actions, which adapt it for purposes
of nutrition. Digestion, therefore, embraces the collective operations
and changes which the food undergoes in the alimentary canal.
The whole digestive track from the mouth to the anus which is situated
just below the tail, is sometimes called the alimentary canal.
The mouth is an oval cavity at the commencement of the alimentary or
digestive canal. In front of the mouth are the lips, one above and
one below; at the sides are the cheeks. The mouth is lined with what
is known as the mucous membrane, in which are several small openings,
from the glands, which are situated about the mouth. Through these the
saliva is poured. On the upper part of the mouth the mucous membrane
is thrown into ridges, or folds, from 18 to 20 in number. This is a
point of importance in connection with bleeding a horse with lampas. It
is never safe to bleed back of the third bar because there is a large
artery which runs down through the roof of the mouth and enters the
hole in the bone just before it reaches this bar. The tongue, which has
the chief nerves of the sense of taste, is situated in the mouth; this
organ also has a very important part to perform in masticating the food
and mixing it with saliva. The teeth, which also take a very active
part in the masticating of food, are dealt with under the heading of
“Teeth.”
SALIVARY GLANDS.--These glands secrete the saliva that is poured into
the mouth while the animal is eating. There are only three pairs of
much importance. One large pair, one on each side of the throat below
the ears, known as the parotid glands, fill up the space between the
jaw bone and the neck. This pair has tubes passing around and under the
lower jaw and up into the cheek muscles entering the mouth opposite
the fourth molar tooth. These tubes, known as steno’s ducts are about
an eighth of an inch in diameter and convey the saliva from the
glands into the mouth. The next pair are situated under the pair just
mentioned. Their tubes enter into the bottom part of the mouth. The
third pair are situated under the tongue, one on each side. They pour
their secretion into the mouth by several small openings near the front
under the tongue. This can be seen by examining the under surface of
the tongue closely. This is very important fluid in connection with the
digesting of the food.
The gullet is a cavity situated just back of the mouth. It is chiefly
made up of muscles which perform the act of swallowing the food. It is
lined with the continuation of the mucous membrane of the mouth.
The oesophagus, or the continuation of the gullet, is a tube extending
from the gullet to the stomach, and is used to convey the food to
that organ. It is made up of two coats, the muscular and the mucous.
The former contains fibers which, when once the food enters the tube,
contract behind it, forcing it down to the stomach. Its lining is a
continuation of the mucous membrane of the mouth and the gullet. In
tracing the oesophagus or tube down the neck from the gullet, note
that it passes down the left side of the neck, entering the thoracic,
or chest cavity, between the lungs over the heart through the large
muscular curtain known as the diaphragm, then enters the stomach an
inch or two after passing the diaphragm.
THE STOMACH.--This organ is very small in the horse in comparison with
that of the ox. It holds only about four gallons, and is situated
just back of the curtain which separates it from the lungs. It lies
mostly to the left side. The walls of the stomach being composed of
three coats. That on the outside is called the serous membrane, a name
applied to membranes which line closed cavities, such as the abdominal
cavity. The inside lining is a continuation of the mucous membrane
lining the organs before mentioned. The lining in the left part of
the stomach or the part where the food is prepared for digestion is
the same color as that of the mouth. The lining of the right part
of the stomach, which is the true digestive part, is of a deep red
color resembling velvet, and when placed under a microscope has the
appearance of a honey-comb. When the stomach is empty this membrane is
thrown into loose folds. Several small openings may be noticed through
which the gastric juice and pepsin from the glands, situated in the
walls of the stomach, enters. These are very important fluids as they
assist greatly in digesting the food. The third coat is known as the
muscular coat already mentioned. Its action is to give the stomach a
churning motion, rolling the food around and mixing it with the juices.
The opening to the stomach is guarded by a valve which prevents the
food from passing back through the gullet. There is also a valve at
the opening of the bowels, preventing any coarse, undigested food
from entering them. The stomach is held in its place by five large
ligaments, and is well supplied by blood-vessels and nerves. Digestion
of the food takes place very quickly in the horse in comparison to
other animals. Frequently a change of food or working too soon after
eating will interfere with the digestion, thus setting up what is known
as indigestion. This is a very painful disease in the horse. After the
food is acted upon by the juices in the stomach it changes into what
is known as chyme, which passes into the bowels.
THE BOWELS.--They are divided into two parts--the large and small.
The small bowels are 72 feet in length, about one inch in diameter,
and are made up of three coats, same as the stomach. The serous coat
on the outside contains small glands which secrete an oily material
to lubricate the outside of the bowels, which comes in contact with
the inner wall of the abdominal cavity. The muscular coat, made up of
muscular fibers, is situated between the other two coats, the same
as in the stomach; its action is to contract the bowels, giving them
motion to convey the food along through them. The mucous coat is a
continuation of the mucous coat of the stomach. Along this coat are
found small glands known as villi lacteal; these absorb the nourishment
from the food as it passes along through the bowels and pours it into
the blood. The small intestines or bowels are attached on the upper
side to what is known as the mesentery, which is attached above to the
roof of the abdominal cavity. It can be seen in any of the smaller
animals upon examination. About six inches from the stomach, in the
bowels, are found two openings. One of these receive the hepatic duct,
a tube for the purpose of carrying the bile from the liver to be poured
in on the food as it passes through the bowels. The other opening is
for the duct of the gland known as the pancreas. It secretes a clear
fluid known as the pancreatic juice. These juices act on the food
in the first part of the small intestines, changing it into chyle.
After this, the action of the rest of the intestines is to absorb the
nourishment out of the food as it is passing back. The small intestines
and stomach, when in a healthy condition, should be found empty one
hour after food has been eaten. The small bowels or intestines are
situated mostly on the left side just behind the stomach.
The large bowels have three coats, the same as the small ones. The
first part of the large bowels is known as the blind bowel or caecum,
and is about three feet in length; this is generally the first thing to
protrude when opening a horse’s abdominal cavity. Its use is to act as
a reservoir to hold the water and fluid of the food; from this organ
the water and fluid parts are mostly taken up into the system. The next
part of the large bowels is known as the large colon; it lays along
the floor of the abdominal cavity, is about nine feet in length and
is doubled on itself three times. In this bowel the solid part of the
food is found. Here digestion is brought about by the contraction and
expansion of the muscles of the bowel and the nourishment taken from
it, after which it is worked back out of this bowel and enters what is
known as the floating colon. This is about ten feet in length and about
two inches in diameter, or double the size of the small bowel. It is
thrown into folds or pleats, and as that portion of the food containing
no nourishment passes through it is worked into balls which pass back
and are emptied into the rectum or back bowel. This is situated at the
back part of the abdominal and pelvic cavity back of the small bowels
or intestines and like them, is suspended by a fold paritoneum.
The rectum or back bowel is sometimes known as the straight bowel.
It is about 18 inches long and forms the last part of the bowels or
intestines. Its coats are a continuation of those of the large bowel,
but each is thicker and heavier. Above this bowel are the bones of the
sacrum, below it, in the horse the bladder and other small glands.
Below the rectum of the mare are situated the womb and the vagina, the
latter being the passage into the womb from the outside. The bones
which help to form the pelvic cavity are situated at the sides, and
at the back immediately under the tail is what is known as the annus.
The use of the rectum is to hold the balls as they pass back from the
floating colon. When the rectum becomes so full that there is pressure
on the sides of the wall thus stimulating the nerves the muscular coat
contracts and forces the contents back towards the annus. At the same
time the muscles of the annus dilate, causing the faeces to pass out.
ACCESSORY ORGANS OF DIGESTION.--In the abdominal region these organs
are the Liver, the Pancreas, and the Spleen.
The Liver is the largest gland in the body and is situated between the
stomach and the diaphragm. The liver of the horse weighs from ten to
twelve pounds. It is of a dark brown color, well supplied with blood
and nerves, and is held in place by several strong ligaments. A bitter,
greenish colored fluid called the bile is secreted from the liver and
emptied into the digestive system, where it plays an important part
in its action on the food. There is no gall bladder in the horse, but
simply a tube passing from the liver to the small bowel into which it
empties the bile about six inches back of the stomach. It is important
to note that it is in this tube that gall stones sometimes collect.
The Pancreas is another very important gland. It is of a grayish, fatty
color, and may be found near the roof of the abdominal cavity in front
of the kidneys. The Pancreas secretes a clear, colorless fluid called
the pancreatic juice. This fluid, like the bile from the liver, also
plays an important part in the digestion of food. It is carried down
from the Pancreas by a duct or tube emptying into the small bowel just
back of that of the liver.
The Spleen is a long, flat gland about fifteen inches in length,
situated along the left side of the stomach and to which it is closely
attached. It is of a grayish red color and feels quite soft. It is
ductless, there being no secretion passing from it. The function of
this gland is not clearly understood, but by many it is supposed to
regulate the temperature of the stomach during the process of digestion
and to act as a reservoir for the blood. Some speak of it as the
burying ground of the red corpuscles. It is well supplied with blood
vessels and nerves and weighs about two pounds in an average sized
horse.
RUMINANTIA.
DIGESTIVE SYSTEM.--The lips of an ox are thick and hard. The upper has
no hair on it and varies in color with the color of the animal. When
cattle are in good health this space is always moist.
The cheeks on the inside are covered by many small rough processes,
which give them a very rough appearance.
The Tongue of the ox is stronger than that of the horse and is more
movable. It is very thick and heavy at the back, pointed at the front
end and the upper part of it is very rough. It is by means of the
tongue that the ox takes most of the food into the mouth.
The Salivary glands are similar to those of the horse.
The Teeth differ very much from those of the horse.
The ox has no front teeth in the upper part of his mouth, their place
being taken by a pad of cartilage or gristle. This pad takes the place
of the upper row of front teeth. The lower row of teeth press against
it when the animal is cropping grass. This accounts for the fact that
cattle do not do as well on short grass as horses.
The front teeth in the lower jaw also differ from those of the horse.
They are eight in number, chisel-shaped, and are loosely set in the gum.
The molars, or back teeth, are similar to those of the horse, only
they are smaller and not so smooth on their upper surface. The ox has
twenty-four molars or back teeth, and eight incisors or front teeth,
making thirty-two in all.
The Gullet of the ox is much larger than that of the horse.
The Oesophagus or tube, which carries the food down from the mouth to
the stomach is well developed, the fibers in it being very strong and
possessing a double action. When the animal is eating they carry the
food from the mouth to the stomach, and when chewing the cud they act
the very opposite, carrying the food from the stomach back into the
mouth.
THE STOMACH.--The student will do well to give some time to the study
of this important organ of the ox, as it is very frequently the seat of
disease.
The stomach has a capacity of fifty-two gallons and is divided into
four separate and distinct compartments: the Rumen or Paunch, the
Reticulum or Honey Comb, the Omasum or Many-plies, and the Abomasum or
the true Stomach. In the first three of these the food undergoes a sort
of preparatory process, while in the fourth the process of digestion is
complete.
The Rumen or paunch is very large, and in an aged animal fills
three-quarters of the abdominal cavity. It lies up against the left
side of the wall of the abdomen, where it is attached and held to its
place by the ligaments. Its situation being an important matter, as
many diseases of the rumen, or paunch, are first noticed on the left
side. Tapping for bloating is always done on the left side because
of this fact. The walls of the paunch of an ox resemble those of the
stomach of the horse, but are not so sensitive, and stand a great deal
of abuse before inflammation sets in. The paunch has two openings, both
of which are at the front; through one the food enters, while through
the other it passes out into the next division.
The Reticulum, or honey comb, is the smallest division and resembles a
honey comb in appearance. This part has little to do with preparing the
food. It is provided with two openings, one in front, where the food
enters, the other at the back, where it passes through into the third
division. In the reticulum, or honey comb, the food is softened further
by the water that the animal drinks which passes directly into the
second division. The food is here pressed into balls and prepared to be
forced back into the mouth to be further masticated.
The Omasum, or many-plies, is the second largest division of the
stomach. When full it is ovoid in shape. It is placed just behind the
second division and at the right side of the paunch. The inside is full
of folds, or layers of membrane, into which all the coarse parts of the
food pass and roll about until it is fine and well prepared to pass
into the last division. When this part of the stomach becomes deranged
and the food becomes dry and hard between the folds, the disease called
impaction of the many-plies, or dry murrain, is the result.
The Abomasum, or fourth stomach, is the true digestive part. In it the
food is completely digested. The walls are redder in color than those
of the three first divisions and contain the glands which secrete the
acids and gastric juices. This stomach has two openings, one through
which the food enters and the other through which it passes into the
small bowels.
The Bowels, or intestines, of the ox are divided into large and small
bowels. This, together with their structure and action resembles that
of the horse. The small bowels are only half the size of the horse,
being about one-half inch in diameter, and about one hundred and fifty
feet in length. The large bowels are not nearly so long as those of the
horse and are thirty-five feet in length.
The Liver of the ox resembles that of the horse, except that it is
provided with a gall bladder which resembles a pear in shape. This acts
as a sac in which to store the gall during the time it is not required
in digestion. When digestion is going on the wall of the gall sac
contracts and forces the gall down to the food. The other glands, the
pancreas and spleen, resemble those of the horse. The juices from these
glands have the same action in cattle as they have in the horse.
RUMINATION, OR CHEWING THE CUD.--Food when first taken into the mouth
of a ruminant is but lightly masticated and mixed with the saliva from
the salivary glands, after which it is swallowed, passing through the
oesophagus into the rumen or paunch (first stomach). This division
acts as a reservoir or storehouse for food thus eaten quickly. When
the animal has time, so to speak, he lies down or stands quietly and
completes the process of mastication of his food by chewing the cud.
This peculiar act is performed as follows: After being softened and
moistened by warmth, the food passes from the rumen or paunch into
the second division--the reticulum, honey comb or second stomach. In
this small globe-like compartment the food is moistened and compressed
into pellets--the cud. By a peculiar reverse action of the oesophagus
or gullet these pellets are taken back into the mouth for further
mastication or chewing. When re-mastication is completed it is again
swallowed, but this time it passes directly into the omasum, many-plies
or third stomach, and thence to the fourth or true stomach.
PROCESS OF DIGESTION AFTER RUMINATION.--Following rumination which,
strictly speaking, is the first step in the digesting process, the food
passes into the third stomach. The fine parts pass right along to the
fourth stomach while the coarser parts are drawn between the folds of
the membrane in this division and worked about until it is fine and
ready to pass into the fourth stomach, where it becomes fully digested
by the action of acids and gastric juices which are secreted in this
part. It then passes into the small bowels, and is acted upon by the
bile from the liver and the pancreatic juice from the pancreas. These
juices are emptied into the first part of the small bowels through
little ducts or tubes, which lead from the glands down to the bowels,
just on the same principle as that of the horse. After this, throughout
the rest of the bowels, the nourishment of the food is taken into the
system by means of little glands which are situated in the coating of
the bowels. The nourishment when once in the blood goes to supply the
different parts of the body, while the part containing no nourishment
or undigested passes off through the back bowels in the form of feces.
TEETH.
Teeth are objects situated in the upper and lower jaws. They are made
of the same tissues as bone but contain 10-1/2 per cent. more of earthy
salts. This fact accounts for their extreme hardness. Unlike bone they
can stand exposure to air and friction without becoming diseased. Teeth
are used to masticate or chew the food, and because of the constant
change in their formation and appearance they serve as a guide in
telling the age of the horse.
There are three hard structures that enter into the formation of the
teeth--Dentine or Ivory, Enamel, and Cementum, or Crusta Petrosa.
The Dentine, or ivory, is situated in the upper part around the pulp or
nerve cavity. It is of yellowish color and largely supplied with nerves
which pass through it from the pulp cavity.
The Enamel is the hardest substance of the tooth, and covers the
outside of all the exposed part. This substance is characterized by its
whiteness and, unlike the dentine, contains no blood vessels or nerves.
If part of the enamel is broken off it is never replaced, and the tooth
below the broken part generally becomes decayed.
The Cementum, or crusta petrosa, is found in the fang or root and the
parts situated below the gum. It is the softest part of the tooth.
Teeth may be simple or compound. Simple as in the dog, where the entire
exposed surface is covered by a solid cap of enamel, which alone is in
wear; compound or complex, as in the horse, where various tissues are
in wear. A tooth consists of the following anatomical parts: The body,
or crown, that part above the gum; the table, the part that comes into
wear on the top; the neck, the part to which the gums are attached; and
the fangs or roots, the parts situated down in the bone.
There are three kinds of teeth found in the horse, the incisors, the
canine and the molars.
The Incisors, or front teeth, situated in the front part of the mouth
just inside the lips, are twelve in number, six above and six below.
The Canine, or bridle teeth, are often absent in the mare. They are
four in number, two in the upper and two in the lower jaw, one on
each side about two inches back from the incisor teeth. They are from
a quarter to three-quarters of an inch above the gum, are round and
pointed and of no particular use. They resemble the eye teeth of other
animals.
The Molars, or back teeth, are twenty-four in number, six on each side
in the upper and six on each side in the lower jaw. With these the food
is ground and masticated.
Wolf Teeth are two small, round, pointed temporary teeth which vary in
size in different animals, situated one on each side in front of the
molars or back teeth in the upper jaw.
TEMPORARY AND PERMANENT TEETH.--The horse has two sets of teeth. The
milk are temporary and are those that the colt sheds; while those that
come in and remain without being shed are called the permanent teeth.
The cutting of the teeth of the foal varies, but at or within nine
days after birth he has four front teeth, two in the center above and
two below, and in the back part of the mouth twelve molars. At from
seven to nine weeks four more incisors or front teeth appear, one at
each side of the two center teeth in each jaw. At nine months he gets
the last of his milk or temporary teeth, these being the corner teeth,
two in the upper side and two in the lower side of the jaw. At this
time he has his full set of milk temporary teeth, consisting of twelve
molars or grinders and twelve incisors or front teeth, six above and
six below, making twenty-four in all. As the colt advances in age he
sheds all these teeth. He then commences to get permanent teeth. When
the age of one year is reached, four permanent molars appear, two in
each jaw, one on each side, behind the three temporary teeth. At two
years of age he gets four more back molars, one on each side of each
jaw. When the age of two years and nine months is reached the two
middle teeth of the temporary incisors, or front teeth of each jaw
fall out, and are replaced by two permanent incisors in each jaw; thus
at the age of three years these four permanent incisors are up and in
wear. At this age, the first eight molars, two on each side of each
jaw, are shed and replaced by eight permanent molars. At four years of
age he sheds four more front or incisor teeth next to those shed at
three years, and these are replaced by four more permanent incisors or
front teeth. At this age, too, he sheds the four remaining temporary
molars, or grinders, which are replaced by four more permanent molars.
He also gets four more permanent molars at the back of the mouth. Thus
at the age of four years the colt has a full set of permanent molars,
consisting of six on each side of each jaw, making twenty-four in all.
At five years of age he sheds the four remaining temporary incisors or
front teeth, which are replaced by four permanent incisors, known as
the corner teeth. It is important to become familiar with the time at
which the colt sheds his different teeth, for sometimes the caps or
shells of the teeth do not fall off when they should. These should be
watched, for they greatly interfere with feeding and should be removed
with forceps. At five years of age the canine or bridle teeth make
their appearance; thus at the age of five years the colt has all his
teeth or what is known as a full mouth.
The following table shows the various changes taking place in the
mouth of the horse from the time of birth up to the age of five years:
Hence the horse has--
--Incisors-- Canine --Molars--
Age Temporary Permanent Temporary Permanent
At or soon after birth 4 0 0 12 0
9 weeks 8 0 0 12 0
1 year 12 0 0 12 4
2 years 12 0 0 12 8
3 years 8 4 0 4 16
4 years 4 8 0 0 24
5 years 0 12 4 0 24=40
The table given below indicates the various changes which occur in
the mouths of ruminants, and more particularly in the mouth of the ox:
RUMINANTS
--Incisors-- --Molars--
Age Temporary Permanent Age Temporary Permanent
At or soon after
birth 4 0 12 0
2 weeks 6 0 1 year 12 4
3 weeks 8 0 2 years 8 12
2 years 6 2 3 years 4 16
3 years 4 4
4 years 2 6 4 and 5 years 0 24=32
5 years 0 8
A table giving the number and variety of teeth as they occur in
the domestic animals and in man may be serviceable as one of handy
reference, and is herewith appended:
Incisors Molars Canine Bicuspid Total
4 6 2 4
Man -- -- -- -- = 32
4 6 2 4
6 12 2 0
Horse -- -- -- -- = 40
6 12 2 0
0 12 0 0
Ox -- -- -- -- = 32
8 12 0 0
6 12 2 0
Dog -- -- -- -- = 42
6 14 2 0
6 14 2 0
Pig -- -- -- -- = 44
6 14 2 0
6 8 2 0
Cat -- -- -- -- = 30
6 6 2 0
The dental formula of the ox is the same as that of all ruminants.
RESPIRATORY SYSTEM OF THE HORSE.
ORGANS OF RESPIRATION.--By the action of these organs certain chemical
and physical changes take place in the blood, the chief of these
consisting of absorption of oxygen from, and giving off carbonic
acid to the atmospheric air, the former change being necessary for
the elaboration of the fluid, the latter for the elimination of a
substance which, if retained, would prove injurious. The organs of
respiration are invariably adapted to the wants of the animal and the
medium in which it lives. Thus insects breathe by air-tubes, opening
on the surface of the body; in the oyster breathing is performed by
fringes; in fishes by gills; in the mammalia by means of elastic
air-receptacles, called lungs, which are enclosed in special cavities,
and communicate with the atmosphere by means of an air-tube.
In the horse, who breathes only through his nose, the organs of
respiration are the nostrils, nasal-chambers, larynx, trachea, and in
the thoracic cavity, the bronchi, bronchial tubes, and the lungs.
NOSTRILS.--The nostrils are two openings, one on each side of the nose.
They are held open by the aid of cartilage and muscles. About one and
one-half inches up the nostril on the under side is a small opening
about the size of a grain of shot. Through this opening the duct or
tube which carries the tears down from the eyes empties into the nose.
The nostril is lined with a thin, delicate skin which changes into
mucous membrane as it passes up into the chambers of the head.
NASAL CHAMBERS.--These give passage to the air from the nostril into
the larynx. There are two of these chambers, divided in the center by a
thin partition or cartilage called the septum nasi. These communicate
with the sinuses of the head. The horse cannot breathe through the
mouth on account of the formation of the throat, and this compels him
to always breathe through the nostrils. This is a point which should be
remembered.
LARYNX.--This is a cavity made of cartilage. It gives passage to the
air and also the organ of voice. It is situated in the floor of the
gullet. This cavity has an opening on its upper side, guarded by a
valve, which is always opened except when the animal is swallowing
food or water. When the food is being swallowed it passes over the
valve which closes the opening while the food passes over it. This is
important, for if the valve does not close properly, thus allowing
either food or water to drop into the windpipe, the animal will have a
fit of coughing. This is sometimes referred to as “the food going down
the wrong way.” On the outside of this cavity of cartilage are found
several small muscles which help to hold it in its place. It is lined
inside by a continuation of the same membrane as that of the chambers
of the head. The vocal cords which come into play when the animal is
whinnying are found along the inside of this cavity. These cords are
not nearly so well marked as in the human being, and if they or the
cartilage of the larynx become affected it generally gives rise to the
disease called wind-broken or roaring.
TRACHEA (Windpipe).--This is a tube which conveys the air down from
the larynx to the bronchial tubes in the lungs. It is made up of forty
or fifty rings of cartilage which are united to each other by strong
elastic ligaments. They give to the windpipe its flexibility, that is,
the power to bend in any direction almost like a piece of elastic. From
the larynx the windpipe enters the chest where it terminates into two
small tubes, one going to the right lung and one to the left. These are
called the bronchial tubes.
BRONCHIAL TUBES AND AIR CELLS.--These are made up of the same material
as that of the windpipe, but are only about half the size. After
passing into the substance of the lungs they break up into small tubes
which pass all through the lungs and terminates into what is known as
the air-cells. These small tubes and air cells are lined inside by a
very thin mucous membrane, a continuation of the membrane lining the
other organs already mentioned. Just inside this thin mucous membrane
is found the capillary network of the lungs, and while the blood is
slowly passing through this network of vessels it gives off to the air
in the air cells carbonic acid gas and takes in the oxygen from the
pure air while it is in the lungs.
LUNGS.--Lungs are the most important organs of respiration. They are
spongy, yellowish organs, two in number, one situated on the right
side, and the other on the left. The right lung is the largest because
of the left one having a hollow in its side for the heart. The lungs
are separated by a partition known as the mediastinum, by the heart
which is in the folds of this partition, and also the large blood
vessels and oesophagus. They are made up of light elastic tissue and
are full of air cells and tubes. While the animal is alive they are
very large and fill up nearly the whole chest cavity, but after death
they collapse and are not nearly so large. Between the lungs and
the ribs is found a serous membrane called the pleura or the lining
membrane of the chest. It is made up of two folds, one being attached
around the outer surface of the lungs, while the other is attached to
the ends of the ribs at the side and at the back to the large curtain
which separates the lungs from the bowels. The little glands situated
in this membrane secrete an oily fluid which serves to lubricate these
parts while the lungs are working in the chest so as not to cause
friction. When this membrane becomes inflamed from a chill or injury it
sets up the disease called pleurisy.
RESPIRATION.--The number of respirations per minute varies with the
different classes of animals; as a rule, the larger the animal the
slower the respiration.
The horse 8 to 10
Cattle 12 to 15
Sheep and goats 12 to 20
The dog 15 to 20
Swine 10 to 15
The rate of breathing is increased from the process of digestion
immediately after eating, or may increase from exercise.
RESPIRATORY SYSTEM OF THE OX.
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.
URINARY ORGANS OF THE OX.
The chief difference in these organs occurs in the kidneys, which in
the ox are larger, and in place of being smooth, like those of the
horse, are rough, resembling a bunch of grapes. The bladder and the
urinary organs resemble those of the horse.
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.
FEMALE GENITAL ORGANS.
The female genital organs, or the organs of the mare, are very much
different from those of the horse. They are known as follows: The
ovaries, the fallopian tubes, or tubes which carry the ovum from the
ovaries to the uterus or womb, the uterus or womb, the vagina, and the
vulva.
The Ovaries in the mare correspond to the testicles in the horse. Each
is about the size of a pigeon’s egg, and resembles it much in shape.
They are held in place by ligaments, and at the back part are provided
with tubes leading from them called the fallopian tubes. The ovaries
secrete the ovum or germ. This is a very minute body, which, when
examined under the microscope, is found to be only 1-150 of an inch in
diameter.
The Fallopian Tubes are two canals, one on each side. They pass
backward and upward, and enter the front part of the uterus or womb.
These small tubes are simply used to carry the germ or ovum up from the
ovaries and empty into the uterus or womb.
The Uterus or Womb is a muscular sac situated in the pelvic cavity,
bounded above by the rectum, below by the bladder, and on either side
by the walls of the pelvic cavity. It is divided into what is known
as a body and a neck. The body of the womb is very small, being only
about four to six inches in length and a couple of inches in diameter
when the animal is not pregnant. Near the front end, at the upper side
there are openings by which the ovum enters. When the animal becomes
pregnant, the body of the womb becomes enlarged and passes forward
and to the left side of the abdominal cavity. It continues to enlarge
as the time of pregnancy passes on, until the foetus, or young, has
attained its full size. After the mare has had her young, the womb
begins to get smaller until it attains its natural size again. The
womb is very largely supplied with blood vessels and nerves. This is
especially so when the animal is pregnant, as it takes a large amount
of blood to nourish the foetus, or the young animal, before birth. It
is made up of three coats. The inner is called mucous membrane, and
in the mare, while pregnant, is covered with numerous processes about
the size of peas to which the placenta or after-birth of the foal is
attached. The muscular coat is next to that of the mucous coat, and
lies between the outer and inner coats of the womb. It is made up of
muscular fibres, and is strong and thick in the womb, much thicker
than it is in the bowels or other organs, already mentioned. This coat
supports and protects the foetus, or young, while being carried in
the womb, and at the time of parturition, or what is commonly known
as foaling, this coat also comes in use. It contracts the womb very
forcibly on the foal, while the neck of the womb lies open, thus
helping to force the foal out of the womb. This is important as the
contraction of this coat produces what is known as labor pains. Lying
outside, and covering around the womb, is a serous coat, a continuation
of the serous coat of the bowels. The womb is held in place by strong
ligaments attached to the sides, and from there to the hip bones. These
are called broad ligaments. At the back part of the womb is the neck.
It consists of an opening, formed by a projection about the size of an
egg. This has a hard, gritty feeling when the animal is not in season.
The neck at this time is closed. The neck of the womb is under control
of the muscle around it, and this muscle is under control of the nerves
of the womb. When a mare comes in season this muscle is relaxed to a
certain extent, thus allowing the neck to open wide enough for the
passage of a couple of fingers. By working around it with the fingers
at this period it can be forced wide enough to admit a man’s hand. If
the mare is put to the horse at this time and becomes pregnant or with
foal, the muscles in the neck of the womb contract, firmly closing
it. It remains closed until the time of foaling. When, at the time
of foaling, the labor pains come on, the muscle in the neck dilates,
allowing the neck of the womb to open large enough for the foal to
pass out. The neck of the womb can be felt easily by oiling the hand
and passing it into the passage of the womb. It will be noticed, too,
that the neck spoken of projects into the passage.
THE VAGINA AND THE VULVA.--These two organs together make up the
passage which leads into the womb from the outside. In the young mare
they are separated by a thin curtain, or partition, made up of mucous
membrane. This curtain is found about four inches from the outside,
and is known as the hymen. It is destroyed, or should be, when the
mare is first put to the horse, although it is broken down other ways,
and in some cases it will disappear of its own accord. The part of
the passage in front of the hymen is called the vagina. This passage,
in structures, resembles the womb, but is not so strong. There are
numerous glands situated along the inner lining which secretes a fluid
to lubricate it. The principle use of this organ is to guide the penis
during sexual intercourse, and at the time of foaling serves as a
passage for the foal. That part of the passage behind the hymen is
known as the vulva. It is about four inches long and about two or three
inches high, varying according to the size of the mare. In front, it
is separated from the vagina by the hymen membrane. It resembles the
vagina in structure and is also provided with little glands in its
inner membrane to secrete fluid to lubricate the passage. At the back
part of the vulva or around the outside is what is known as the lips
of the vulva, one on each side of the opening. The outside of the lips
is covered by a very fine skin. Just below the skin, they consist of
erectile tissue, which is the same kind of tissue as that of the penis
of the horse. This tissue is found more abundantly in the lips of the
vulva of the young mare than in those of an old mare. The opening
between these lips is situated just below the anus, or the opening
where the back bowel ends. At the back part of the vulva, on the under
side, is an opening, or hole, about large enough for the passage of
a man’s finger. Through this hole the tube leading from the bladder
enters into the passage and allows the urine to pass into the vulva,
through which it runs out of the body. The clitoris is situated on the
upper side of this passage, just inside the lips. It can be seen in
the mare when she works the vulva after passing urine. Just below the
clitoris are found two or three small glands which secrete the fluid
that passes away when the mare is horsing.
Mammary Glands, or what is known as the mare’s udder or bag, are two
in number, situated between the thighs. In the young mare they are
very small, but after the mare is pregnant a few months these glands
enlarge, until at foaling time they attain their largest size. They are
covered outside by a thin, smooth skin. The substance of them consists
of small glands and tubes retain or hold milk until it is drawn away
from the bag either by milking or by the young animals sucking. During
the time of suckling the young, the glands are largely supplied with
blood, from which the milk is secreted. On the under side of each
gland is found the teat, or that part taken hold of by the young when
sucking. The end of the teat is pierced by several small holes, through
which the milk passes.
GENITAL ORGANS OF THE BULL.
The testicles are ovoid in shape and well developed, its long axis
being nearly vertical; the membrane which separate the two testicles is
very strong.
The spermatic cord and artery are small compared with those of the
horse.
The penis is long and pointed, and has an S-shaped curve in it just
below the pelvic bones; this curve can be felt by feeling just behind
the bag.
The sheath is long and runs further forward on the belly. It has a tuft
of hair on the point of it. During the time the bull is serving the
S-shaped part of the penis is straightened out by the action of the
protracter muscles, and drawn back into the S-shaped curve by retractor
muscles.
The urethra is completely enveloped by the fibrous sheath.
GENITAL ORGANS OF THE COW.
The ovaries of the cow are comparatively smaller than those of the
mare, but resemble them in structure.
The uterus or womb of the cow somewhat resembles that of the mare, but
the inner membrane is different, being covered with sixty or eighty
mushroom-like bodies about the size of a pigeon’s egg, more flattened
out. These bodies receive the name of cotyledons; to these the placenta
or afterbirth is attached--a very important point with which every
person interested should be familiar. These may be felt by examining a
cow soon after calving. The passage from the womb of the cow is shorter
than that of the mare, but is formed on the same principles.
The mammary glands constitute an organ termed the _udder_, which is
composed of two symmetrical halves, placed one against the other. Each
half is again divided into two distinct glands, each with its own
teat, so that the udder consists of four mammae and four teats; behind
this there may be two small rudimentary teats. In the center of each
quarter, just at the base of the teat, is a large cavity, the general
receptacle of all the milk ducts. From this cavity, which is sometimes
large enough to contain a quart, proceeds down the center of the teat
one defined canal from which the milk is drawn.
In the small ruminants as the sheep and goat there are two mammae and
two teats, constructed like those of the cow.