The Digestive System 151 



spending 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 into its 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 CEsopHAcus 



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 oesophagus is smooth and 

 muscular while the lining is thrown into numerous 

 longitudinal folds that in the empty oesophagus 

 nearly obliterate the lumen ; where distended by food 

 or pebbles the longitudinal folds may be almost 



