(ESOPHAGUS, STOMACH, AND INTESTINE. 



233 



The large intestine has a straight course, is often consider- 

 ably swollen, and opens into a cloaca. An account of the allan- 

 tois of the Amniota will be found in a subsequent chapter 

 (p. 273). 



From the Eeptilia onwards a process (generally asymmetrical) 

 of the anterior portion of the large intestine is usually formed, 

 giving rise to a caecum or blind -gut. 



The function of the bursse anales of Chelonia, which consist of paired 

 csecal outgrowths of the cloacal wall, is not understood. 



Birds. In correspondence with the kind of nutriment, the 

 mode of life, and the absence of teeth, a division of labour occurs 

 in the stomach of Birds, which, instead of remaining simple, 

 generally becomes divided into two portions, an anterior and a 



Oe 



FIG. 191. DIAGRAM OF THE (ESOPHAGUS AND STOMACH OF A BIRD. 



Or, Oe 1 , oesophagus ; Ig, crop ; DM, glandular stomach ; MM, muscular stomach ; 



MD, duodenum. 



posterior. The former (Fig. 191, DM), which, on account of its 

 richness in glands, is called the glandular stomach (proventri- 

 culus), alone takes part in dissolving the food; while the latter 

 (Fig. 191, MM], which is lined by a horny layer consisting of a 

 hardened glandular secretion, has simply a mechanical function, in 

 correlation with which a very thick muscular wall provided with 

 two tendinous disks is developed. 



The latter portion is for this reason spoken of as the muscular 

 stomach, or gizzard, and the degree of its development stands 



