6'i- Mammalia. Digestive System, 



wider above than below, formed by a continuation of tbe 

 integument of tbe nasal cavity and of tbe moutb, and ex- 

 tending from the base of tbe skull : it has 'seven openings 

 leading into it : at its upper part, in front and above the 

 level of the soft Palate, are the two posterior Nares, and, 

 on each side, the apertures of the Eustachian tubes ; below 

 the soft palate is the isthmus of the Fauces, opening into 

 the Mouth : posterior to the root of the tongue is the opening 

 into the Larynx protected by the Epiglottis : lastly, the con- 

 tracted part of the funnel forms the (Esophageal opening. 



The (Esophagus is nearly cylindrical ; it is generally long 

 and narrow, and forms the narrowest part of the Intestinal 

 Canal : after passing into the Abdomen through a slit in the 

 Diaphragm it usually expands at once to form the Stomach : 

 its muscular coat consists of two layers ; the external fibres hav- 

 ing a longitudinal direction; the internal fibres surrounding 

 the canal generally in a circular or spiral manner : its mucous 

 membrane and the innermost covering of Epithelium form, 

 usually, longitudinal folds which become more conspicuous on 

 contraction of the muscular coat : it is rarely provided at its 

 termination with valvular spiral folds : but as a rule passes 

 to the stomach without any valve. The Qj]sophagus of Mam- 

 malia is never wholly destitute of a Sheath of striated muscular 

 fibre (as is that of Sauropsida)*. 



The Abdomen, as a definite and circumscribed visceral 

 chamber, is peculiar to the present class ; the Heart and 

 other thoracic viscera being shut out by the complete trans- 

 verse septum or * Diaphragm ' from the major part of the 

 trunk cavity. 



The Stomach presents remarkable diversities. In the 

 greater number of Mammalia it is simple as in Man, though 

 frequently with the pyloric portion reverted. Sometimes 

 the Cardiac portion is divided from the Pyloric by a constric- 



* Gulliver, 



