456 ANATOMY OF VERTEBRATES. 



the pressure of the contents of the stomach, when acted upon by 

 the powerful muscular coat, the oesophagus enters in a valvular 

 manner, and is surrounded at its termination by a great accession 

 of muscular fibres, forming a coat of an inch or more in thickness : 

 the outermost of these fibres run longitudinally ; the middle ones 

 decussate each other obliquely ; the innermost are circular and 

 form a sphincter round the cardia. The diameter of the canal so 

 surrounded is but 3 lines and its inner membrane is gathered 

 into irregular transverse rugae. That of the cardiac compart- 

 ment is puckered up around the cardia, whence a few small 

 irregular rugae extend along the lesser curvature and about 

 the constriction leading to the pyloric compartment: over the 

 rest of the surface the membrane was not folded and was finely 

 reticulate. At the constriction, ib. c, there is an accession of 

 circular muscular fibres and a valvular production of the inner 

 membrane about 3 lines broad. Immediately beyond this cir- 

 cular fold are the orifices of the two caecal appendages, ib. d, 

 d: they are relatively narrower than in the Manatee : their 

 lining membrane is minutely rugous : there were comminuted 

 fuci in both; their muscular coat is 1| lines thick: they are, 

 in some Dugongs, of unequal length. The pyloric stomach, 

 ib. b, is long and narrow, and extends a foot beyond the caecal 

 appendages before terminating in the pylorus, ib. g : the inner 

 membrane presented a few rugae : the cavity is bent upon itself, 

 and the terminal part, g, is intestiniform, but with thick walls. 

 The small intestines, in a half-grown Dugong, presented a length 

 of 27 feet and a uniform diameter of 1 inch: they have a 

 similar uniformity in the Manatee. In the Dugong the mucous 

 membrane, beyond the pylorus, is for a few inches slightly rugous, 

 and then becomes disposed in transverse wavy folds : at 5 inches 

 from the pylorus the duodenum receives the biliary and pancreatic 

 secretions on a mammillary eminence. Beyond this part the 

 transverse rugae are crossed by longitudinal ones, and the surface 

 becomes sub-reticulate : this disposition extends along about 6 

 feet of the gut, when the transverse disposition subsides, and the 

 longitudinal folding prevails throughout the rest of the small in- 

 testine. The muscular coat is 2 -J- lines thick, the external longi- 

 tudinal layer being about half a line. The orifices of intestinal 

 follicles are arranged in a zig-zag line, thus .•.•.•.*.* upon 

 the mucous surface along- the side of the intestine next the me- 

 sentery, all the way to the caecum, fig. 357. Where the ileum, 

 ib. a, enters that cavity it is surrounded by a sphincter as thick 

 "as that at the cardia. The caecum is conical; in my half-grown 



