DIGESTION. 77 



cells, it has seveival convolutions, and its diameter varies at 

 different parts. 



This peculiar structure eminently qualifies it for retaining its 

 contents, so as to perfect the process of digestion ; for it appears 

 that the large intestines in the horse effect a more important 

 service than in man or carnivorous animals, a much greater 

 portion of nutriment being absorbed in them. From the colon 

 the faces pass into the rectum in the form of balls of a tri- 

 angular shape, having been so modified by the latter part of the 

 colon. 



The rectum, as its name implies, is a straight gut acting as a 

 reservoir for the faeces, and is furnished with a powerful mus- 

 cular coat, by the contractions of which it is, from time to time, 

 expelled ; with the assistance, however, of the diaphragm and the 

 abdominal muscles. 



The intestines, both large and small, are fastened to the spine 

 by means of a strong membrane, whicli is spread out in a radiated 

 direction, like a fan, the foci of which are of course towards the 

 spine. That part of the membrane which is attached to the small 

 intestines is termed the mesentery ; and the other portions are 

 termed the mesocolon and the mesorectum, according to the gut 

 with which it is connected. This membrane, which we may as well 

 designate as the mesentery throughout, not only serves to sustain 

 the bowels, but also to afford a vehicle for their important vessels. 

 Thus we have numerous arteries for the nourishment of the coats 

 of the bowels, and to furnish their internal secretions. We have 

 likewise the mesenteric veins, which have been found not only 

 to return the venous blood, but also to have a power of absorbing 

 the more fluid contents of the bowels, as well as some chemical 

 agents which have been administered for experiment, and which 

 the lacteals have refused. There is also an abundant supply of 

 nerves passing to the bowels, furnishing them with nervous 

 energy, and keeping up their connection with the sensorium. 

 These are not only nerves of sensation, but also of involuntary 

 motion : the former are at all times the medium of common 

 feeling, and sometimes, as in spasms or inflammation, the source 

 or seat of the most intense pain ; the latter endow the muscular 

 coat of the bowels with the peculiar peristaltic or vermicular 

 action it possesses, and by which the contents are passed onwards. 

 Lastly, the mesentery abounds with minute vessels, called the 

 lacteals, which open into the intestines, and absorb the chyle, 

 and convey it through a number of glands, called mesenteric 

 glands*, to a canal denominated the receptaculum chyli, which 

 takes its course along the spine, and terminates in a large vein, 

 just before it reaches the heart. The lacteals are so small as to 



* These glands sometimes become hardened and enlarged, and thus inter- 

 rupting the course of the chjle, causes the animal to lose flesh. 



