312 SPLANCHNOLOGY, 



LEVATOR ANL 

 (Fig. 100. g.) 



This name has been apj)lied to a kind of small muscular liga- 

 ment which joins the rectum to the coccyx above. 



RETEACTOR ANI. 



Situated on the side of the anus, this is a broad, flat, and 

 powerful muscle, arising from a rough margin just behind the 

 acetabulum, and the inner surface of the sacro-sciatic ligament. 

 It is inserted to the lateral aspect of the anus, its fibres blending 

 with the sphincter. 



Action. — To retract the anus. 



The anterior mesenteric artery supplies the caecum and great 

 colon, the posterior mesenteric artery supplying the rest of the 

 large intestine, assisted by the internal pudic. The blood is 

 returned by the mesenteric veins to the portal vein. The nerves 

 come from the mesenteric and hypogastric plexuses. 



The caecum seems to be a reservoir for the large quantities of 

 fluid swallowed by the animal. In it and in the great colon 

 absorption of fluid takes place, but the bulk of the ingesta which 

 are passed into the floating colon consists of residual or fsecal 

 matter, having been deprived of its nutritive principles. Hence 

 the floating colon may be regarded as being partly, the rectum 

 entirely, an excretory organ. 



Accessory Organs of Digestion. 



In the abdominal region these organs are the Liver, the 

 Pancreas, and the Spleen. 



LIVER. 



The liver is a solid gland, situated in the abdomen, extending 

 from the right, through the epigastric, to the left hypochondriac 

 region. It is the largest secreting gland in the body, weighing 

 from ten to twelve pounds, and in shape is very irregularly 

 elliptical, thick in the centre, gradually thinning at the borders, 

 and presenting numerous clefts ; it has two surftices and a cir- 

 cumference. The anterior surface is smooth, convex, and cleft 

 by a deep vertical fissure, in which lies the posterior vena cava. 



