ALIMENTARY CANAL OF RODENTIA. 



421 



the pyloric aperture is much larger than the cardiac one and is 

 bounded toward the left side by a valvular ridge. 



In the Squirrels (Sciurus) the stomach is of a pyriform or 

 oval shape, quickly contracting to a conical or cylindrical por- 

 tion, which is bent upon the small curve and terminates in the 

 pylorus. The cardiac compartment, which projects far to left 

 beyond the oesophagus, is lined with a thick epidermis, which 

 forms two oval lips, as it is prolonged around the opening into 

 the second compartment, the lining membrane of which is gastro- 

 mucous. 



In the Hamsters (Cricetus) the stomach is divided into two 

 pouches, separated by a deep constriction; the left pouch is 

 cylindrical, the right globular. The cardiac orifice is situated in 

 the constriction, so that food can pass at once into the pyloric 

 compartment and be antiperistaltically moved and stored in the 

 cardiac division. 



In the Rat (Mus decumanus) the abdominal part of the gullet, 

 fig. 317,/, is 11 inches long, and carries forward a fold of peri- 

 toneum. The cardiac compartment, ib. a, has thin coats and is 

 lined by an epithelium which usually gives it a whiter colour than 

 the rest of the organ. At the midpart, ib. Z>, there is a tendinous 



319 



Stomach of the Water-vole, cxxn' 



Stomach of the Lemming, inner surface, 

 cxxxni". 



patch from which muscular fibres radiate, as in the bird's stomach : 

 the muscular coats of the pyloric division, d, are thicker, as is also 

 the gastro- vascular lining membrane. 



In the Water-vole (Arvicola amphibius) the cardiac and middle 

 compartments form one elongated cavity, fig. 318, «, f 9 sepa- 

 rated by a constriction from the pyloric portion, b. This swells 

 out in two directions, above into a small sacculus, e, the coats of 

 which are thin, like those of /, and below into the true digestive 

 pyloric part, with a thicker muscular tunic and gastro-vascular 

 lining membrane. The epithelial lining of a } f, terminates by a 



