82 ANATOMY OF THE RABBIT. 
fossae, and also with the middle ear through the internal auditory 
tube, and a ventral or laryngeal portion, containing the aperture 
of the larynx (Fig. 41). 
The oesophagus is a slender but greatly expansible tube leading 
from the pharynx to the stomach. In its passage backward it 
traverses the neck and the thorax, and in both regions occupies a 
median position. In the thorax (Plate VII) it will be observed 
that it lies between the heart and the dorsal aorta, thus exhibiting 
the original relation of the digestive tube ‘to the aortic portion of 
the vascular system. The succeeding portions of the digestive 
tube are those associated with the peritoneal cavity, and with the 
exception of the terminal portion, the rectum, are displaced from a 
median position. Consequently, the divisions which are recognized 
are based partly on the differential characters of the wall, and partly 
on the position of structures more especially in relation to the 
supporting peritoneum. Thus, the chief features of the stomach 
(Fig. 42) depend on the expansion of the organ and the rotation 
of its pyloric end forward and to the right. In the intestinal tract 
as a whole the chief, although by no means most conspicuous feature 
of position, depends on the looping of the entire structure on itself, 
so that the terfhinal portion, chiefly the transverse colon, crosses 
the ventral surface of the duodenum and then turns backward on 
the dorsal surface of the mesenterial small intestine. The duo- 
denum is sharply marked off from the mesenterial intestine as an 
extensive loop, containing the major part of the pancreas and its 
duct, and lying on the right side of the dorsal wall of the abdomen. 
The common bile duct enters its first portion immediately 
beyond the pylorus. The mesenterial intestine is a greatly 
convoluted portion, lying chiefly on the left side of the abdominal 
cavity, and loosely supported by the broad, frill-like mesentery. 
From the pylorus to the sacculus rotundus there is no abrupt change 
in the character of the wall, although the first portion of the mesen- 
terial intestine, that designated as the jejunum, and the duodenum 
may be considered together as a more vascular portion with thicker 
walls in comparison with the second portion, the ileum, in which 
the wall is less vascular and more transparent. 
The main portion of the large intestine, the colon, although 
greatly specialized, may be considered to consist as in man of 
