which is located on the concave, or attached, side of the spleen. The
splenic artery, upon entering the organ, at once branches, the trabeculæ
forming a support for the vessels.
After the arteries have entered the hilum, as stated above, they divide
into many branches which follow the septa of the connective tissue. At
first the arteries are accompanied by branches of the splenic veins.
Soon, however, the arteries leave the veins and the septa, and penetrate
the splenic pulp. In the splenic pulp the adventitia of the smaller
arteries assume the character of reticular tissue, and become
infiltrated with lymphoid cells. This infiltration forms masses which
are called the splenic corpuscles, or Malpighian bodies. The terminal
arteries break up into capillaries, which still retain an adventitia,
and empty into border spaces, or sinuses, sometimes spoken of as
ampullæ. These sinuses in turn empty into cavernous sinuses of the
splenic pulp. From these are finally formed the venules; and the
collections of venules form the splenic veins through which the blood
gains exit from the spleen.
=The Abdominal and Pelvic Cavities.=—In birds the abdominal cavity is
divided into two smaller cavities by a fibrous septum. The anterior
cavity representing the abdominal contains the liver, and the other
representing the pelvic contains the gizzard, intestines and oviduct.
=The Peritoneum and the Mesentery.=—The abdominal and pelvic cavities
are lined by the peritoneum. Like all serous membranes this is composed
of a parietal and a visceral portion, which together form a complete
sac, with the organs it covers situated on the outer side. The
peritoneum like other serous membranes consists of a mesothelial and a
submesothelial portion, the cells of the former being arranged in a
single layer. Since a serous membrane is so arranged as to line a closed
cavity, and at the same time to cover its contents, it follows that the
entire membrane must be a closed sac, the mesothelial layer being on the
inside; such a sac is called a serous sac, or cavity. Synovial membranes
are also regarded as a variety of serous membranes. The fold, or layer,
of the membrane which lines the cavity is called the parietal, that
which covers the greater part of the organs contained therein is called
the visceral portion; the two surfaces contacting, and gliding upon each
other, are lubricated by a fluid secretion contained in the sac; hence
one use of these membranes is to prevent friction between the walls of
cavities and the organs contained therein. Serous membranes line the
abdominal cavity, pericardium, cavities of the heart and is continuous
throughout the vascular structures.
[Illustration:
FIG. 39.—A transverse section of body of hen through 15, Fig. 34. _R_,
Right side. _L_, Left side. 1, Spinal cord. 2, Esophagus. 3,
Trachea. 4, Skin. 5, Pectoral muscles.
]
The serous membrane besides covering the external surface of the
viscera, double folds pass from one organ to another, or from an organ
to the parietes of the cavity. These double folds of the peritoneum are
known as ligaments, or as mesenteries. In ligaments the two folds are
strengthened by an interposed layer of fibro-elastic tissue. A
_mesentery_ is a broad, double fold of peritoneum, attached to the
abdominal parietes above, and containing a portion of the intestine in
its free or remote extremity. Between its folds we find blood-vessels,
nerves, and lymphatics or lacteals, hence it permits vascular and
nervous communications with the organ attached to it. The free portion
of the small intestine is attached to the free margin of the mesentery.
THE RELATIONS OF THE VISCERAL ORGANS OF THE DOMESTIC FOWL
[Illustration:
FIG. 40.—Transverse section through the body of a hen through 14, Fig.
34. _R_, Right side. _L_, Left side. 1, Spinal cord. 2, Esophagus.
3, Trachea near inferior larynx. 4, Lungs. 5, Pectoral muscles.
]
Figure 33 shows a fowl with the left abdominal wall and the left
thoracic wall removed. No. 1 in this figure shows the base of the heart
in front of the left lobe of the liver. Above the liver is the
proventriculus; above this, the diaphragm; and above the diaphragm and
the base of the heart the left lung occupying the superior part of the
thoracic cavity, and that there is no distinct pleural sac, as in
mammals but that the lung pushes out between the ribs, thus pressing
against the ribs on the inner and the lateral sides. The gizzard is back
of the liver, to the left side of the abdominal cavity, and beneath and
in front of the duodenal loop. The small intestine from this side is
above the gizzard. Supero-anterior to the gizzard is the blind end of
the cæcum. The pancreas is within the duodenal loop.
[Illustration:
FIG. 41.—Transverse section through the body of a hen at 12, Fig. 33.
_R_, Right side. _L_, Left side. 1, Spinal cord. 2, Esophagus. 3,
Inferior larynx. 4, Base of the heart. 5, Aorta. 6, Vena cava. 7,
Lungs. 8, Skin. 9, Pectoral muscles.
]
Figure 34 shows the viscera from the right side after the removal of the
right abdominal and the right thoracic wall. The base of the heart is in
front of the right lobe of the liver. Above these the right lung
occupies the upper part of the thoracic cavity as in the preceding
illustration. Just back of this is the anterior lobe of the kidney. The
gall-bladder is observed at No. 9 on the right lobe of the liver. Just
inferior to a longitudinal central line is the duodenal loop, between
the limbs of which is seen the pancreas. Above this loop the cæca are
located. The gizzard is not visible from the right side; on this side
posterior to the liver is the small intestine. Superior to this at No. 7
the rectum.
The relative position of the visceral organs in the median line is
observed in Fig. 35. No. 1 of this figure shows the stump of the first
portion of the esophagus, and No. 2, the left wall of the crop.
Following this, and located just below the vertebræ is the second
portion of the esophagus. The major portion of the crop is located on
the right side.
[Illustration:
FIG. 42.—Transverse section through the body of a hen at 11, Fig. 33.
_R_, Right side. _L_, Left side. 1, Spinal cord. 2, Vertebra. 3,
Spinous process of vertebra. 4, Lungs. 5, Esophagus. 6, Pericardial
sac. 7, Sectioned surface of heart. 8, Auricle of heart. 9, Blood
clot in right auricle. 10, Section of sternum. 11, Pectoral muscles.
]
It will be noted that the second portion of the esophagus passes over
the base of the heart and the superior part of the liver, and then
terminates in the proventriculus. The proventriculus extends downward
and empties into the gizzard. This organ lies antero-laterally to the
gizzard, supero-posterior to the liver, and to the left of the spleen.
The spleen lies in a triangle formed by the liver, the proventriculus,
and the gizzard. The heart is noted to lie supero-anterior to the liver,
and between the anterior portion of the fissure formed by the right and
the left lobe. The ovary is located back of the diaphragm at the
anterior end of the kidney and below the inferior surface of the bodies
of the vertebræ. The bulk of the floating portion of the small intestine
is located above the gizzard.
[Illustration:
FIG. 43.—Transverse section through the body of a hen at 13, Fig. 34.
_R_, Right side. _L_, Left side. 1, Spinal cord. 2, Body of
vertebra. 3, Superior spinous process of vertebra. 4, Lungs. 5,
Esophagus. 6, Heart. 7, Right and left lobes of liver. 8, Sternum.
9, Skin. 10, Pectoral muscles.
]
A transverse anterior section of a normal laying hen is shown in Fig.
39, the section being made at 15 of Fig. 34. At this point the esophagus
lies centrally and above the trachea. Figure 40 shows a transverse
anterior section through the thoracic region at 14 of Fig. 34. At this
point the esophagus is slightly to the right of and is superior to the
trachea. At this level the apex of the lung is sectioned. This is in the
region of the cervical air-sac. Figure 41 shows a posterior section at
12 of Fig. 33. The esophagus here is above and to the right of the
inferior larynx, and directly below and between the lungs. The inferior
larynx is above the base of the heart.
Figure 42 shows a transverse anterior section made at 11 of Fig. 33. It
shows that at this level the esophagus is centrally located and passes
over the base of the heart. The heart occupies the lower portion of the
thorax and the lungs the upper. Figure 43 shows a photograph of a
transverse anterior section of the body made at 13 of Fig. 34. At this
level the apex of the heart lies within the anterior fissure of the
liver. The sectioned portion of the heart shows the lower portion of the
ventricle.
[Illustration:
FIG. 44.—Transverse section through the body of a hen at 12, Fig. 34.
_R_, Right side. _L_, Left side. 1, Spinal cord. 2, Articular
surface of vertebral segment. 3, End of rib. 4, Lungs. 5,
Proventriculus. 6, Liver showing Glisson’s capsule. 7, Sternum. 8,
Pectoral muscles. 9, Skin.
]
[Illustration:
FIG. 45.—Transverse section through the body of a hen at 10, Fig. 33.
_R_, Right side. _L_, Left side. 1, Spinal cord. 2, Body of
vertebra. 3, Lungs. 4, Ova. 5, Proventriculus. 6, Liver. 7, Sternum.
8, Skin. 9, Pectoral muscles.
]
In this figure the lungs show, on the sectioned surface, the ends of
some of the larger bronchi. The esophagus is located above the heart.
Showing the relations of the visceral organs back of the heart girdle,
photograph number 44, gives an anterior section made at 12, Fig. 33. The
lungs are spread out occupying the posterior thoracic region and below
at No. 10 is the diaphragm. The diaphragm does not appear to have that
rigidity and firmness of position as in mammals. It is rather
rudimentary. Below the left lung and above the left lobe of the liver is
the proventriculus. Note that the viscus is empty and that the mucous
membrane is thrown into folds. At this point the liver occupies much of
the abdominal cavity. Figure 45 is a view of an anterior section made at
10, Fig. 33. In this section the lungs are decreasing in caliber. The
liver occupies much of the space in the lower right abdominal quadrant,
and above and to the right is the ovary with many of the ova developing
yolks. Below No. 4 which is a developing yolk, is the proventriculus.
Figure 46 is a view of an anterior section made at 9, Fig. 33. At this
level are shown sectioned surfaces of the kidneys, which lie on either
side of the spinal column. Below the spinal column and occupying the
left upper quadrant is the ovary containing ova in the process of
developing yolks. To the right is the sectioned surface of one of the
cæca and below this and on the right side is the sectioned ends of many
of the loops of the floating portion of the small intestine. Occupying
the left lower quadrant is the sectioned surface of the gizzard and on
the abdominal floor and to the right of the gizzard, the posterior end
of the right lobe of the liver.
[Illustration:
FIG. 46.—A transverse section through the body of a hen at 9, Fig. 33.
_R_, Right side. _L_, Left side. 1, Spinal cord. 2, Vertebra. 3,
Kidneys. 4, Ovary. 5, Cæcum. 6, Small intestine. 7, Gizzard. 8,
Right lobe of liver. 9, Skin. 10, Pectoral muscles.
]
THE RELATIONS OF THE VISCERAL ORGANS OF THE BABY CHICK
There is approximately 47 per cent. of the yolk retained in the
abdominal yolk sac of the baby chick at hatching. Figure 47 shows a
photograph of a longitudinal section through a baby chick. This figure
shows all the posterior portion of the abdominal cavity occupied with
abdominal yolk. The abdominal viscera are pushed forward, and as the
yolk is gradually absorbed the visceral organs gradually occupy their
normal position.
[Illustration:
FIG. 47.—An antero-posterior section through the body of a baby chick
just hatched. 1, Abdominal yolk sac. 2, Gizzard. 3, Liver. 4, Heart.
5, Intestines. 6, Spinal cord. 7, Cerebrum. 8, Cerebellum. 9, Fat in
the post-occipital region. 10, The thymus gland.
]
[Illustration:
FIG. 48.—Transverse sections of the body of a baby chick at hatching.
_R_, Right side. _L_, Left side.
_A._ A transverse section at _A_, Fig. 50. 1, Spinal cord. 2,
Esophagus. 3, Entrance to thorax. 4, Stubs of the wings.
_B._ A transverse section at _B_, Fig. 50. 1, Spinal cord. 2,
Esophagus. 3, Lungs. 4, Heart.
_C._ A transverse section through the body at _C_, Fig. 50. 1, Spinal
cord. 2, Lungs. 3, Esophagus. 4, Liver. 5, Heart.
_D._ A transverse section at _D_, Fig. 50. 1, Spinal cord. 2,
Proventriculus. 3, Liver. 4, Gizzard. 5, Intestine. 6, Kidneys. 7,
Gall-bladder.
]
[Illustration:
FIG. 49.—Transverse section through the body of a baby chick.
_E_ at _E_, Fig. 50. 1, Spinal cord. 2, Kidneys. 3, Gizzard. 4,
Intestines. 5, Unabsorbed yolk. 6, Stubs of legs.
_F._ A section at _F_, Fig. 50. 1, Spinal cord. 2, Kidneys. 3,
Intestine. 4, Unabsorbed yolk.
_G._ A section at _G_, Fig. 50. 1, Anus. 2, Umbilicus.
]
A section through this body Fig. 47 at _A_ is shown in Fig. 48, _A_. At
this point the esophagus appears below the vertebral column. Figure 48,
_B_, a section through the body at Fig. 47, _B_, shows the apex of the
lungs. In a median line and below the lungs is the esophagus. Note the
mucous membrane thrown into folds. Here the heart is sectioned, showing
both auricles and both ventricles. This is a view looking forward.
Figure 48, _C_, is a view of a posterior section made at Fig. 47, _C_.
It shows the same relations of the esophagus and lungs, but shows at
this level both the right and the left lobe of the liver. Between these
lobes we note the sectioned apex of the heart. Figure 48, _D_ shows a
posterior section at Fig. 47, _D_. At this level the kidneys are above
and infero-laterally to the spinal column. The intestines are below the
kidneys; and on the left side, between the kidneys and left lobe of the
liver, and near the abdominal wall, is the proventriculus. Occupying the
major portion of the inferior abdominal cavity are the right and the
left lobe of the liver, and between these the anterior border of the
gizzard. Note the gizzard sitting at an angle inclining toward the left
side. Figure 49, _E_ shows a section at Fig. 47, _E_. Here the gizzard
occupies the left lower abdominal quadrant. To the right are the
intestines; and directly above the gizzard is a small portion of the
anterior end of the abdominal yolk sac. Infero-laterally are the
kidneys. Figure 49, _F_, shows the kidneys similarly located as in the
preceding; and just below is the rectum suspended by the mesentery. The
rest of the cavity is occupied by the abdominal yolk.
THE URO-GENITAL SYSTEM
The uro-genital apparatus, or apparatus uro-genitalis, consists of two
groups of organs: the urinary and the genital. The former elaborate and
remove the chief excretory fluid, the urine; and the latter serve for
the formation, development, and expulsion of the products of the
reproductive glands.
THE URINARY APPARATUS (Fig. 50 and Fig. 51).
The urinary apparatus of the bird consists of two kidneys, from each of
which a ureter extends and empties into the cloaca.
=The Kidneys.= _Location._—The kidneys are located in excavations in the
pelvic roof. They are related internally with the posterior aorta and
vena cava, supero-internally with the lumbo-sacral vertebræ and
superiorly and supero-externally with the ilium. The abdominal visceral
organs lie below the kidneys. The kidneys are external to or above the
peritoneum.
_Shape._—In the fowl of average size the kidneys are 2½ inches long and
are made up of three irregular lobes. The anterior lobe is usually the
largest and the middle the smallest. The anterior border of the first
lobe is located opposite the last true dorsal articulation. The anterior
lobe is called the anterior pelvic or ilio-lumbar lobe, the middle the
middle pelvic or ilio-sacral lobe, and the posterior the posterior
pelvic lobe.
_Structure._—The whole kidney has a fine transparent covering. The dark,
brownish-red parenchyme can be seen through this membrane. It has a
blood vascular system and a urinary tubular system. The larger arteries,
the veins, and the nerves pass between the lobules, and the smaller
vessels between the tubules. These form fine network or plexuses. The
lymphatic vessels are very few, and are mainly found on the surface. The
kidneys are pierced in their posterior third by the external iliac
artery and at about its middle by the venous branches forming the
posterior vena cava.
The lobes are made up of _lobules_, which are plainly perceptible from
the external surface. Each lobule is apparently a unit within itself. It
receives its blood supply from small branches of the renal artery and is
made up of a cortical or peripheral portion which contains the
glomerules (Fig. 52, _A_) and a medullary portion, which is made up of
tubules, or urinary canals, arteries, veins, and nerves.
[Illustration:
FIG. 50.—Photograph showing spinal cord and relative positions of the
kidney, lung and heart. 1, Heart. 2, Lung. Note the indentations
made by the ribs. 3, The anterior, middle and posterior lobes of the
kidney. The lobules are plainly visible. 4, The lumbo-sacral segment
of the spinal cord. 5, Terminal cord filament. 6, The cervico-dorsal
segment of the spinal cord. 7, The brachial nerve plexus. 8 and 9,
The lumbo-sacral plexus. 8, The ischiadic nerve. 9, The lumbar
nerves.
]
The _urinary canals_ are divided into two kinds, namely, the outer and
the inner tubular systems. The outer canals, called the _tubulæ
uriniferi corticalis_, are very small in caliber and are located in the
lobules. The renal artery (Fig. 53, No. _B_, 3) breaking up into
arterioles in the kidney, and finally reaching the cortical portion of
the lobules, form capillary plexuses in the shape of minute spheres,
which are the glomerules (Fig. 53, No. _C_, 3 and _B_, 5). Around each
glomerule there is formed a capsule called _Bowman’s capsule_, which is
the beginning of the uriniferous tubule. This entire mass is called the
_Malpighian body_, or _renal corpuscle_. This capsule then extends as
the urinary, or secreting tubule, being at first constricted, then
convoluted, and terminates into a second portion, the _descending limb
of Henle_. This portion of the tubule becomes constricted. It then forms
the loop of Henle and ascends as the second portion, or second limb of
Henle, which is again of greater diameter. The top of the secreting
tubule is slightly wavy and empties into the collecting tubule along
with many others. These collecting tubules in turn merge into large
tubules which finally empty into the ureter (Fig. 53, No. 14). These
collective bundles correspond to the pyramids of the kidneys of mammals.
[Illustration:
FIG. 51.—The kidneys. 1_a_, The posterior. 1_b_, the middle and 1_c_,
the anterior lobes of the kidney. 2, The posterior aorta. 3, The
external iliac or crural artery. 4, The ischiadic artery. 5, The
sacralis media artery. 6, The ureter which empties into the cloaca
at 7. 8, The external iliac vein. 9, The internal iliac vein. 10,
The iliacus communis.
]
[Illustration:
FIG. 52.
_A._ Photomicrograph of a section of a kidney showing three lobules.
1, Cortical portion of lobule showing glomeruli. 2, The central or
medullary portion of the lobule. 3, The outer surface of the kidney.
_B._ Salts from the urine of a hen. 1, Uric acid crystals. 2. Sodium
urate crystals.
]
[Illustration:
FIG. 53.—The renal structure.
_A._ 1, Capillary blood-vessel. 2, Descending limb of Henle. 3,
Collecting tubule. 4, Ascending limb of Henle.
_B._ 1, Branch of renal artery. 2, The descending or medullary branch.
3, The ascending branch. 4, The arteriole taking part in the
formation of the glomerule. 5, The glomerule. 6, Bowman’s capsule.
7, Blood-vessel extending from the glomerule. 8, The vein of the
medullary part of the lobule. 9, The neck. 10, The convoluted
tubule. 11, The descending limb of Henle. 12, Henle’s loop. 13, The
ascending loop of Henle. 14, The collecting tubule.
_C._ 1, Section through a convoluted tubule. 2, Bowman’s capsule. 3,
The glomerule.
]
The neck of the uriniferous tubule as it emerges from Bowman’s capsule
is short and narrow and is lined with a few cuboidal cells. Toward the
glomerular end the cells are of a transitional form gradually merging
into the flat squamous type peculiar to Bowman’s capsule. The first
convoluted tubule is lined with irregular cuboidal or pyramidal
epithelial cells. The descending limb of Henle’s loop is narrow and is
lined with a simple layer of flat epithelial cells. In the loop the
epithelium changes from the flat type in the descending limb to the
cuboidal in the ascending limb. The ascending limb of Henle’s loop again
becomes broader and is lined with low cuboidal cells. The second
convoluted, or tortuous, tubule is lined with low cuboidal cells as are
also the collecting tubules. The collecting tubules originate from every
part of the internal substance of the lobules, and extending to the
gyrations, uniting in the pinniform structure and traversing to the
margin of the lobules, following along the uneven surface,
infero-laterally and toward the median body line, finally empty into the
ureter.
There are many arterial branches given off from the arteria renalis. The
arteries which supply the kidneys are given off from the posterior aorta
and ischiadic artery. As soon as these arteries enter the kidney they
break up into two systems. One system supplies the kidney substance with
nourishment in the form of nutrient blood; the second system supplies
the glomerules with what may be considered functional blood (Gadow). The
second system of arteries branches into the small arteria
interlobularis, which pass between the lobules of the kidneys where they
give off side branches which penetrate the cortical portion of the
lobules and form the capillary plexus, the glomerule.
The arteriole that enters into the structure of the glomerule is lined
with endothelial cells and is surrounded by a few muscle fibers and a
fine network of connective tissue. The vessel that carries the blood
away is similarly constructed.
_Function._—In the glomerules the liquid portion of the urine is
filtered out of the blood, which urine flows through the uriniferous
tubules and passes from the kidney through the ureter. In the cubical
cells are extracted the solid portions of the urine which also pass
through the tubules with the liquid. The urinary secretion, as found in
the ureter, does not contain much liquid, but, on the contrary, is made
up of a pasty material consisting of salts which are, for the most part,
uric acid crystals and sodium urate (Fig. 52, _B_). This material
becomes hard, like cement, soon after being exposed to the atmosphere.
This secretion may be noted as a whitish pasty material on the outer
parts of the feces, or droppings, voided by the birds.
=The Ureter.= _Location._—The ureter extends along the inferior surface
of the kidney. It has its origin near the anterior extremity of the
kidney, and passing posteriorly the entire length of the kidney receives
tributary collecting tubules, and terminates in the upper wall of the
cloaca in the urodeumal portion.
_Shape._—The ureter gradually enlarges in diameter until it reaches the
posterior border of the kidney, and then maintains about the same
caliber throughout the rest of its course.
_Structure._—The ureter wall is made up of three coats as follows:
mucous, muscular and fibrous.
_Function._—The ureters serve as a passage way for the urine from the
kidneys to the cloaca.
THE MALE GENERATIVE ORGANS (Fig. 54)
The male generative organs in the fowl consist of two testicles and an
excretory apparatus, the vas deferens, for each.
=The Testicles.= _Location._—The testicles are located in the sublumbar
region of the abdominal cavity, behind the lungs, below the anterior
extremity of the kidneys, and opposite the last three ribs.
[Illustration:
FIG. 54.—The pelvic organs of a cockerel. _A_, Testes. _B_, Rectum.
_C_, Cloaca. _D_, Vas deferens. _E_, Kidney. _F_, Adrenal gland.
_G_, Lungs. _H_, Ureter.
]