ALIMENTARY CANAL 



259 



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

 intestine which contains the spiral valve. In Protopterus} 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 



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, ax, Epithelial cells in the amoeboid state ; b.v, blood-vessels ; cm, 

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

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

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

 visceral layer of the peritoneum ; Siii, 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.^ 



Internal to its peritoneal investment the wall of the alimentary 

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



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



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



' Owen, Aiiat. Phys. Vertebrates, London, 1866, i. p. 424. 



