268 



COMPARATIVE ANATOMY 



structures known as the crypts or glands of Licberkuhn. as well as 

 to acinous mucous glands. Mucous-secreting goblet cells are 



BM M 1 Z IS 



a 



\ 



FIG. 214. A, SEMIDIAGRAMMATIC TRANSVERSE SECTION or A PORTION OF THE 

 WALL OF THE INTESTINE. (Combined from the condition seen in both lower 

 and higher Vertebrates. ) B, Epithelial cells of the intestine. 



/*, peritoneal investment of the gut ; M, longitudinal muscular layer ; M 1 , circular 

 muscular layer ; Z, connective-tissue layer ; S, mucous membrane, which is 

 raised to form villi at Zo. (The connective-tissue layer and epithelium are 

 designedly drawn much too large relatively as compared with the outer 

 coats.) G, G, vessels, the larger trunks running between the peritoneum 

 and the muscular layer ; the finer vessels branch out into the intermediate 

 layer ; these surround the masses of lymph-cells, LL, as well as the glands, 

 and send fine loops into the villi (at O l ) ; DD, apertures of the. glands ; 

 E, E, epithelial cells of the mucous membrane, with their striated border, 

 from which at E l amoeboid processes are extruded : in Fig. B, a, 6, these 

 cells are drawn to a much larger scale (Sa, striated border) ; Ly, scat- 

 tered lymph-cells in the intermediate layer ; L l , L*, lymph-cells in the act of 

 passing through the mucous membrane ; at L' : , several have already passed 

 into the alimentary cavity ; LL, masses of lymph-cells (solitary follicles) ; 

 Lym, lymph -vessels in the villi. 



common throughout the alimentary epithelium of Vertebrates. 

 In Monotremes, as already mentioned (p. 265), gastric glands are 

 absent, but the intestinal glands are highly developed. 



