12 
MAMMALIAN ANATOMY 
of the trachea from its contact with the oesophagus and severing 
the trachea immediately posterior to the larynx. By using the 
cut end of the trachea as a stem and cutting the larger blood 
vessels from their connection with the heart, the whole set of 
organs to be removed may be detached from the membranes which 
hold them in place and lifted out as one mass. The oesophagus 
is thus exposed throughout its entire course, and may be seen to 
pass through the diaphragm and lead into the stomach. 
Turn the whole intestinal mass to one side and find the pos¬ 
terior region of the digestive tract which continues as the rectum 
through the dorsal region of the pelvic cavity to the anal orifice. 
Note that in this region, where the intestine takes a straight course, 
one sees clearly the typical relationship of the parietal and 
visceral portions of the peritoneum continuous with each other 
through the double layers of the mesentery. In the greatly elon¬ 
gated and convoluted region of the intestine the mesentery 
becomes correspondingly elongated along the edge where it joins 
the visceral peritoneum of the intestine so that it is like a very full 
ruffle bearing the intestine along its edge. Note the extensive 
branching of blood vessels which lie between its two layers. In 
regions where different portions of the mesentery come per¬ 
manently in contact extensive adhesions occur. 
Beginning with the rectum trace the whole course of the intes¬ 
tinal tract anteriorly (opposite to the direction of motion of its 
contents) freeing it little by little from its attachment to the 
mesentery until the vicinity of the stomach is reached. Leave the 
loop of the intestine into which the stomach leads, intact in con¬ 
nection with its mesentery. 
The parts of the digestive system may now be studied con¬ 
secutively from anterior to posterior end. Record by drawing. 
(The mouth, pharynx, and salivary glands will be studied in 
greater detail with the sheep’s head and other material later in the 
course.) • 
Note the extent of the oesophagus, the muscular character of 
its walls, and its collapsed condition when empty. 
Note that the stomach is a pouch-like expansion, the develop¬ 
ment of which has involved a rotation into a transverse position so 
that the mesentery of the stomach has formed a sac-like structure 
