DIGESTIVE SYSTEM. 259 



operation is aided by the muscular coat of the intestine itself, 

 which, for that purpose, is possessed of stronger fibres than the 

 others. 



Organization. — The large intestines receive their supply of 

 biood from a vessel of less size than the one going to the small ; 

 viz. i\\Q posterior mesenteric artery. It is a branch from the pos- 

 terior aorta ; and its distribution is similar to that of the anterior 

 mesenteric. The veins end in the vena portae, and possess no 

 valves. The nerves belonging to these intestines issue from the 

 mesenteric plexus. 



OF THE LIVER. 



The liver is the largest gland in the body : it performs the 

 function of secreting bile. 



Situation and Connexion. — Already given at page 247. 



Figure. — Its figure varies somewhat, but not a vast deal, in 

 different domestic animals: it is convex upon its anterior sur- 

 face ; concave upon its posterior; is thick in substance about its 

 middle parts ; but in general declines to attenuated edges around 

 its circumference. It is cleft in various places. These clefts are 

 deeper, and the edges are thinner, in general, in quadrupeds than 

 in the human body. 



Colour. — A reddish brown : its hue will vary according to the 

 quantity of blood there may be in the gland. 



Division. — By its clefts or Jissures, the liver is divided into 

 what are called its lobes ; of which division there is a great va- 

 riety in the different species of quadrupeds. In the horse the 

 gland is constituted of two principal lobes, right and left, united 

 by a middle or intervening portion, and two lobuli, or small or 

 accessory lobes. 



Lobes. — The right, the larger of the two principal lobes, is 

 situated entirely within the right hypochondrium. Proceeding 

 from Its obtuse border, along its concave part, is seen one of the 

 lobules — the lobulus caudatus — which is nothing more than a 

 sort of triangular portion of liver included within the fold of the 

 right ligament. The other lobule possessing a circular border 

 with several clefts or fissures through it, whence it may be de- 

 nominated the lobulus scissatus, issues from the anterior and 

 under part of the middle portion. The left lobe, nearly equal in 

 size to the right, has the general outline of an oval: indeed this 

 figure would be perfect, were it not interrupted by the union of 

 the lobe with the middle portion. 



Peritoneal Covering. — Every part of the liver (with the excep- 

 tion of the spaces occupied by the coronary ligament and pos- 

 terior vena cava) is so closely invested by peritoneum, that the 



