142 



INTRODUCTION. 



tudinal bands ; and, at somewhat more than five inches from the first 

 caecum, a second caecum presents itself, consisting of a pyramidal pouch, 

 of about three inches in length. (See Anat. of Wombat) by Prof. Owen, 

 in Proceedings of ZooL Soc. for 1836 ; p. 49, et seq.) 



Among the Edentata, in the Dasypus Peba, there is merely a slight 

 dilatation of the colon, at the entrance of the ilium, but no true caecum ; 

 in the Dasypus sex-cinctus there are two short but wide caeca, between 

 which the small intestine enters the colon ; in the Myrmecophaga didac- 

 tyla there are two small oval caeca ; while in the Myrmecophaga Tamandua 

 there is no caecum. (See Cuvier's Lecons ; also Meckel.) There is no 

 caecum in the Sloths, which animals, as already stated, have the stomach 

 complicated. 



In the Rodentia there is much diversity, as regards the caecum, 

 between the different genera, as well as in respect of the length of 

 the intestinal canal. In some, the large intestines exceed the small in 

 length ;* and, in most, the caecum is of enormous volume, far exceeding 

 the size of the stomach ; while the colon forms a kind of loop, or dupli- 

 cature, folding upon itself for a considerable distance, as in Capromys, 

 Coipus, Octodon, c. In the genus Myoxus (Dormouse) there is no 

 caecum. In the Hares, Lagomys, Ancema, Agoutis, and Paca, the 

 caecum is very large, and sacculated by tendinous bands : in the genera 

 Mus, Bathiergus, Cricetus, Arctomys Sciurus, Dipus. &c. it is simple. 

 In the Hares, the caecum is at its maximum of development and com- 

 plication, its volume exceeding, by ten times, that of the stomach. 



It would appear to be a general rule, that those of the Rodentia, such 

 as the Hares, which feed upon herbage, or succulent vegetable aliment, 

 have the longest and largest caecum ; that those which live upon grain, 

 as the Campagnols, the Hamsters, and the Lemmings, f and which are 

 very voracious, have also a caecum of great size, though, perhaps, in- 



* Meckel observes, " In general, it may be established, that, among the rodents, the small intestines 

 are relatively shorter than the other portion. In the Beaver, the Mus amphibius, and Bathiergus, 

 the two portions are nearly of equal length ; or, -when there is a difference, they are as sixteen to fif- 

 teen, or as eight to seven. The proportion is still greater, as three to two, in the Beaver ; it is as 

 two to one in the Arctomys, the Hare, the Arvicola, and the Cricetus ; as five to one in the Hystrix, the 

 Ccelogenus, the Cavia ; as three to one in Pteromys, Hydrochoerus, and Sciurus ; as five to one in 

 Mus rattus, Mus musculus ; and, lastly, as five to one in Dasyprocta." 



In Octodon, the small intestines are two feet six inches in length ; the caecum, three inches ; the 

 colon and rectum, one foot five inches and a half ; the length of the head and body together, seven 

 inches. In Capromys Fournieri (measuring, in the length of the head and body, one foot six inches), 

 the small intestines are seventeen feet ten inches; the caecum thirteen inches ; colon and rectum (?) 



In the Coipus, measuring, from nose to root of tail, one foot eleven inches, the small intestines 

 were ascertained to be sixteen feet four inches ; the caecum one foot eleven inches ; the colon and 

 rectum four feet four inches. 



t In the Lemming, the caecum is long (four inches), and sacculated at the base, whence it narrows 

 to an acute apex. Length of the small intestines, two feet six inches ; of the large, one foot seven inches 

 and a half. Length of the head and body of the animal, four inches and three quarters. The large 

 intestine, or colon, commences in the form of a loop, spirally twisted in its course, so as to appear 

 much shorter than it is in reality. From Nutes of Diss. of Lemming, by the Author. 



