140 INTRODUCTION. 



arterial, venous, lymphatic, exhalant, and elaborative ; and, were the 

 heaviest exhausted of the fluids it contains, it would become a light 

 and shrivelled mass. 



The small intestines, in most Mammalia, are very distinct from the 

 large intestines, into which they lead. The large intestines commence 

 by a pouch, more or less voluminous, termed the caecum, or caput 

 caecum coli : from this is continued the colon, often sacculated by bands 

 of muscular fibres running along its surface, contracting it into a series 

 of globular or ovoid pouches. From the lower part of the abdomen 

 (the iliac region), on the right side, where the caecum is placed, it mounts 

 up and crosses the upper part of the abdomen, under the edge of the 

 liver, sweeps down the left side, and, making a flexure (termed sigmoid, 

 from its resemblance to the Greek letter Sigma), assumes the name of 

 rectum. The internal lining is a mucous tissue, often disposed into val- 

 vulae, as in the human subject. 



The caecum, in its volume and structure, bears, like the stomach 

 and intestinal canal (especially the small intestines), an immediate 

 relationship to the nature of the animal's diet. Other circumstances being 

 not contradictory, it may be taken as a rule, that animals existing ex- 

 clusively on vegetable food, have the caecum larger than those of car- 

 nivorous, or partly carnivorous, appetite : its state of complication, 

 moreover, is often in a sort of opposition to that of the stomach. Thus, 

 the diet being alike, animals with a very complicated stomach have the 

 caecum proportionately simple ; others, on the contrary, which have the 

 stomach simple, have the caecum not only very voluminous, but even 

 complex. 



The presence of a caecum, and a definite division between the large 

 and small intestines, do not prevail in all Mammalia ; and, in most cases 

 where the intestinal canal is thus simplified, it is comparatively short. 

 In the Jnsectivora, in the Bears, Racoons, Coatis, and their allies, also in 

 the Polecats and in the Otters, there is no caecum, nor any rigid division 

 between the small and large intestines. In the Seals the caecum is either 

 wanting or it is very small ;* but in these piscivorous animals the in- 

 testinal canal is long. In the canine and feline races the caecum is of 

 inconsiderable development. 



In the Cetacea, the intestinal canal is simple, but elongated ; being, to 

 the length of the body, as eleven or twelve to one : there is either no 

 caecum, or it is very rudimentary. Hunter states that, in the Balaena 

 rostrata, a small pointed caecum exists, like that of the Lion. In the genus 



* In a specimen of the common Seal which the author had an opportunity of examining, a 

 small caecum existed ; the large intestines scarcely exceeded the small in circumference ; the total 

 length of the intestinal canal was fifty-two feet; the stomach was large; the pyloric portion elon- 

 gated, and bent suddenly upon the cardiac. 



