ALIMENTARY CANAL 



259 



is said to be present in connexion with that part of the 

 intestine which contains the spiral valve. In Protopterus, 1 and 

 also in Neoceratodus? there is a well-developed ventral mesentery 

 in relation with the greater part of the length of the intestine, 

 although in the former Dipnoid its continuity is interrupted by 



cm. l.m. 



FIG. 157. Transverse section through a portion of the wall of the intestine, combined 

 from the condition seen in both the higher and the lower Vertebrata. Semi- 

 diagrammatic, a.c, Epithelial cells in the amoeboid state ; b.v, blood-vessels ; c.m, 

 circular muscular layer ; g, one of Lieberkiihn's glands in the higher Vertebrates ; i.ep, 

 intestinal epithelium ; I, leucocytes ; I', leucocytes in the intestinal epithelium ; l.f, 

 lymph follicles ; l.m, longitudinal muscular layer ; lym, lymphatic vessels ; p, 

 visceral layer of the peritoneum ; sm, the submucosa ; v, villi of the higher Verte- 

 brates. (From Wiedersheim.) 



one or two vacuities, and in the latter the mesentery is incom- 

 plete posteriorly. A ventral mesentery is also present in the 

 intestinal region of some of the Muraenidae among Teleosts. 3 



Internal to its peritoneal investment the wall of the alimentary 

 canal consists in succession from without inwards of (1), a 



1 Newton Parker, Trans. Roy. Irish Acad. xxx. 1892, p. 140. 



2 Giinther, Phil. Trans. 161, 1871, pp. 542-543. 



3 Owen, Anat. Phys. Vertebrates, London, 1866, i. p. 424. 



