The Digestive System I51 
sponding fold, the velum palatinum, from the lower 
side of the palate and completely shuts off the 
mouth from the openings of the trachea and gullet 
(Fig. 33). Into this hinder chamber open the 
posterior nares, so that the animal can open its 
mouth under water without getting water into 
its trachea; or it may, while holding its prey in 
its mouth, come to the surface to breathe, without 
danger of letting water intoits trachea. The nasal 
passages, leading from the nostrils to the posterior 
nares, are, of course, completely inclosed by bone, as 
described in connection with the skull. Ventral 
to the larynx and posterior part of the mouth is the 
large, shield-shaped hyoid apparatus, Fig. 25, h, 
also described in connection with the skull. 
THE CESOPHAGUS 
The oesophagus, Fig. 34, e, is long and of about 
the same diameter throughout except possibly for 
a slight enlargement of the anterior region where it 
leaves the pharynx. The two “olivary enlarge- 
ments’? mentioned by Chaffanjon (15) are not 
always present, and when seen were found to 
contain either food or small stones or both. 
The outside of the cesophagus is smooth and 
muscular while the lining is thrown into numerous 
longitudinal folds that in the empty cesophagus 
nearly obliterate the lumen; where distended by food 
or pebbles the longitudinal folds may be almost 
