3. Displacing the liver craniad, the stomach is seen dorsad of its left
lobe. It may extend dorsad of the right lobe, its size depending on the
degree of distension.
4. The duodenum or first part of the small intestine leaves the stomach
at its right side craniad and makes a U bend, the head of which is
directed caudad; it then turns toward the middle line dorsad of the
remaining part of the small intestine.
5. The great omentum is a thin fold of peritoneum with many bands of
fat. It passes like a curtain from the great curvature of the stomach
ventrad of the coils of the small intestine (ileum). It is tucked
beneath the mass of coils at the sides and caudally, and folds of it
extend between the individual coils. Turn it craniad and note--
6. The numerous coils of the third part of the small intestine or
ileum. Turn these to one side and note--
7. The connection of the ileum with the duodenum across the middle
line. An indefinite part of the intestine between the ileum and duodenum
is called the jejunum, because in man it is found empty after death.
8. The passage of the ileum into the side of the large intestine which
begins on the right side just caudad of the loops of the duodenum. The
first part of the large intestine is the colon. It may be traced first
toward the head (ascending colon), then sinistro-caudad (transverse
colon) and then caudad (descending colon). The descending colon returns
to the middle line and the large intestine then continues to the anus as
the rectum.
The blind pouch of the colon which lies caudad of the opening of the
ileum is the cæcum.
9. Turn the duodenum toward the left and note the pancreas, a light
red, elongated organ which stretches along the greater curvature of the
stomach and thence between the two lines of the duodenal U to its
bottom.
10. The spleen, parallel to the gastric portion of the pancreas. It is
deep red (darker than the pancreas and not so brown as the liver) and is
held against the great curvature of the stomach by a part of the great
omentum.
11. The kidneys, close against the dorsal body wall and in contact with
the caudal part of the liver.
12. The bladder, in the median line at the caudal end of the cavity,
held in place by the suspensory ligament, which passes to the midventral
line, and by the lateral ligaments.
13. The mesenteric glands, large grayish-red glands one to four
centimeters long, more numerous in the mesocolon.
14. In the female, lying against the ventral surface of the rectum, the
uterus. It divides into two horns which diverge. Near the end of each
horn the ovary.
15. The peritoneum. Study and understand the description of it (p. 218).
Dissect some of it free from the body wall. (Trace the folds by aid of a
diagram and model.)
B. In the thoracic cavity:
1. The lungs. Each is divided into lobes, three on the left, four on
the right. The caudal right lobe pushes the mediastium toward the left
and thus lies in a pocket dorsocaudad of the heart and dorsad of the
vena cava inferior.
2. The pleuræ. Each pleura is a membrane like the peritoneum. It covers
the diaphragm and the thoracic walls and is reflected onto the lungs.
Hence it is divided into costal and pulmonary portions. Read the
description (p. 217) and trace their connection. Each pleura forms a
closed sac.
3. The mediastinal septum or median vertical portion formed by the
apposition of the medial walls of the two pleural sacs. It divides the
thorax into halves.
4. In the mediastinum or space between the halves of the mediastinal
septum are seen--
_a._ Ventrally (i.e., in the anterior mediastinum), blood-vessels and
fat, and craniad the pink thymus gland. Read the description of the
thymus (p. 254, and Fig. 107).
_b._ Dorsally (i.e., in the posterior mediastinum) the trachea (best
seen craniad), the œsophagus (best seen caudad), and the aorta.
_c._ In the middle (reckoning in a dorsoventral line) (i.e., in the
middle mediastinum) the heart, with the inferior vena cava approaching
it from the rear. Prick into the mediastinum and inflate it. Remove the
thoracic wall opposite the one already removed, so as to stretch the
mediastinum and show it more clearly. Expose the trachea beneath the
caudal end of the sternomastoidei. Note the thyroid gland (Fig. 96, 6,
p. 229). Insert a blowpipe without injury to the thyroid, and inflate
the lungs. Cut the sternum at its caudal end and turn it craniad,
cutting the mediastinal septum and noting its double character.
Dissect the mediastinal septum from the thymus so as to expose this
organ.
_d._ The pericardium, a relatively thick-walled sac, within which the
heart lies. The pericardium is covered by the mediastinal septum on each
side, but not dorsally and ventrally. Dissect the mediastinal septum
from the pericardium. Prick and inflate the pericardium. Open it and
expose the heart.