THE DIGESTIVE SYSTEM 53 



crowd out the other constituents of the 

 membrane. Eberth has described an elevated 

 body in each caecum, about 4 mm. from its 

 mouth, entirely composed of lymphoid tissue. 



The cloaca is the tubular cavity opening on 

 the exterior of the body and common to the 

 digestive and uro-genital tracts. It is divisible 

 into three parts. With the first, the coprodceum, 

 the large intestine (rectum) is continuous ; 

 in the middle part, the urodceum, the ureters 

 and the genital ducts terminate ; and from 

 the dorsal wall of the third and most external 

 part, the proctodceum, an opening leads into 

 a blind, rounded, and unpaired sac, the bursa 

 of Fabricius. The function of the bursa is 

 not clear, but it is known that it has its largest 

 development in the fowl of about four months 

 old, and that from this time it gradually 

 shrivels until hardly any vestige remains by 

 the time the animal has attained the age of 

 one year. The fully developed bursa is lined 

 by a folded membrane, and contains sac-like 

 diverticula in its walls. 



The large, dark-brown or chocolate-coloured 

 liver (Figs. 12 and 22) lies ventral and caudal 

 to the heart. Two lobes, connected by a 

 comparatively narrow isthmus, are readily dis- 



