ALIMENTARY CANAL OF RODENTIA. 425 



applies an expanded termination to a much smaller orifice at the 

 side of the caecum : the part so included forming the valve. The 

 length of the caecum is thirteen inches : its widest circumference 

 six inches : its parietes are puckered up by two longitudinal mus- 

 cular bands, one of which is continued a short way upon the colon. 

 The caecum is marked off from the colon by a valvular structure 

 similar to that at the end of the ileum ; the two orifices of the blind 

 gut being analogous to the cardia and pylorus of the stomach. 1 



In the Coypu the duodenum commences with so large a dila- 

 tation that it projects toward the oesophagus like a caecum ; its 

 circumference here was 4^ inches; the decrease is gradual, 

 and where the biliary duct enters the circumference is three 

 inches, and a little distance below this 2$. The length of the 

 small intestines is sixteen feet, their mean circumference If inches. 

 The caecum is large, making a circular turn at its base and 

 gradually diminishing in volume : it is puckered into sacculi by 

 two muscular bands, less defined toward the basal part: its 

 length is one foot ten inches, its greatest circumference eight 

 inches. The ileum terminates in a sort of sacculus at the base of 

 the caecum, close to the colon. This gut begins large, but gradu- 

 ally becomes narrow : it is slightly sacculated for a short dis- 

 tance : its mean circumference 2| inches. The colon makes an 

 abrupt turn from the caecum, and after a course of one foot five 

 inches suddenly folds upon itself, the reflected length running 

 down for the distance of eleven inches, when it turns as suddenly 

 back again, but does not adhere so closely to the previous fold as 

 that to the first length ; it then contracts and soon proceeds to 

 constitute the rectum. Near the end of the first loose fold, as in 

 Capromys, the faeces begin to assume a solid form in separate 

 oval masses. The total length of the large intestines was four 

 feet four inches. The enormous caecum of the Capybara occu- 

 pies almost the posterior half of the abdomen. 



The parallel course of the arteries along the coats of the colon 

 in Hystricidce, Chinchillidce, and Ctenomyidce, connected at dis- 

 tant intervals by transverse branches, without other ramification, 

 is worthy of remark. 2 In the Porcupine the caecal sacculi are 

 puckered upon three longitudinal bands, two of which are con- 

 tinued some way along the colon. In the Chinchilla the sacculi 

 project alternately from opposite sides of the caecum. The above- 

 defined general form of large intestines in vegetarian rodents is 

 exemplified in fig. 321, from the Water-vole. Here the ileum 



1 cxxx". p. 70, et seq. for further details of the alimentary canal of this rare rodent. 



2 xx. vol. i. p. 215, No. 723, c. cxxxj". p. 22, pi. i. 



