444 ANATOMY OF VERTEBRATES. 



distinctly defined ; in other Reptiles it is indicated by its relation 

 to the pancreas and to the ducts of this gland and the liver, as at 

 e, f, fig. 301 {LacertcL), fig. 306, c,d{Rana), and fig. 305 (Chelone). 

 The large intestine is definitely marked ofi^ in all Reptiles, but is 

 short and, in most, simple, straight, and without caecal production 

 at its beginning;. 



In no Reptile is the intestine so short and straight, or so 

 long and convoluted, as in certain Fishes ; as a general rule, 

 it is shorter in proportion to the trunk than in warm-blooded 

 Vertebrates. 



In the Siren and Amphiume the intestine makes a few short 

 turns in its longitudinal course, and expands into a straight and 

 wide colon or rectum.' In the Menopome^ the convolutions are 

 more numerous, and the rectum is relatively wider. In Ccecilia 

 the intestine is continued in a slightly convoluted manner to the 

 short rectum which opens near the hinder extremity of the snake- 

 like body. The Newts and Salamanders have short intestines, 

 with few coils ; so likewise have the Toads and Frogs ; but, in 

 tlie lar\'al state of the latter, the intestine is very long, and forms 

 a double series of spiral coils, fig. 42, i ; and the modification by 

 absorption of this lierbivorous type of gut to the carnivorous one is 

 not amono; the least of the marvellous changes which the anourous 

 Batraehian undergoes in passing to its adult condition. In most 

 Serpents the short intestinal folds are packed closely together in a 

 long mass by connecting cellular tissue. In Sea-snakes (Hi/drophis) 

 the convolutions are more free. In Lizards the intestinal con- 

 volutions are commonly few, fig. 301, i, fig. 303, g, and free. In 

 the Chelonia, figs. 302 and 304, the convolutions of the small gut 

 are larger and more numerous; they are also well marked" in 

 the Crncodilia. 



The muscular tissue of the intestine shows an external layer of 

 longitudinal fibres, and an internal layer of circular ones ; the 

 latter is remarkably thick in Chelorie. In gillcd and tailed 

 Batrachia the mucous membrane presents fine undulatory longi- 

 tudinal rugffi, not parallel, but often uniting. In Toads the ruga? 

 are transverse at the jejunum : in Frogs the ruo-a; are zio-zan-. 

 The mucous membrane of the intestine presents, in the Python, 

 small, flattened, scale-like processes ; in some Serjients they are 

 longitudinally extended, and fringed at the margin ; the appearance 

 of circular or 'connlvent' valves is due to the close coils of the 

 gut within a common peritoneal slieath. In the Chamarleon tlic 

 intestinal rugro are rhomboidal, and their free border is minutely 



' XX. vol. i. p. 122, prep. r.o. 444. -- n,. ,,. 003, p,op. ,»,. ,-,.'i4. 



