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 (Lacertd), fig. 306, c, d(Rana), and fig. 305 ( Chelone). 

 The large intestine is definitely marked off 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. 1 In the Menopome 2 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 

 the larval 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 herbivorous type of gut to the carnivorous one is 

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

 Batrachian 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 (Hydrophis) 

 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 Crocodilla. 



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 Chelone. In gilled and tailed 

 Batraclda the mucous membrane presents fine undulatory longi- 

 tudinal rugae, not parallel, but often uniting. In Toads the rugae 

 are transverse at the jejunum : in Frogs the rugae are zigzag. 

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

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

 longitudinally extended, and fringed at the margin ; the appearance 

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

 gut within a common peritoneal sheath. In the Chamaeleon the 

 intestinal rugae are rhomboidal, and their free border is minutely 



1 xx. vol. i. p. 122, prep. no. 444. * lb. p. 203, prep. no. 654. 



