VERTEBRATA. 63 



intestine, with the exception of part of the duodenum and 

 the rectum, has been removed. The duodenum hangs down from 

 the gizzard, and contains within its primary convolution the 

 compact pancreas, with the three ducts by which its secretion is 

 poured into the intestine. In addition, two other ducts, one of 

 considerable size, and the other very small, are seen leaving the 

 liver and joining the duodenum. These are the hepatic ducts. 

 The right testis is also to be seen, as a large ovoid whitish body. 

 A little beneath and behind the testis is the tri-lobed kidney. 

 Each of its lobes lies in a depression in the under surface of 

 the ischium. The ureter emerges from its inner edge, and 

 passes posteriorly to its cloacal outlet. A little to its outer 

 side is the sinuous vas deferens. The rectum hangs down 

 from the bottom of the specimen, and about an inch from the 

 anus two small conical caeca join it. On the dorsal surface of 

 the extreme tip of the tail is the uropygial gland, consisting of 

 two pear-shaped lobes. The biceps muscle of the right leg should 

 be noticed passing downwards from the ischium. It passes 

 through a pulley-like loop of tendon at the back of the knee to 

 its insertion in the tibia. 



Class MAMMALIA. 

 Order EODENTIA. 



97. A Rat (Mus decumanus), dissected to shew the dis- 

 tinctive features of its class. 



In addition to the more important anatomical details, the 

 following external points should be noticed : the hairy skin, 

 the existence of distinct outlets for the urinary and generative 

 organs as well as for the intestine, the vibrissaa on the snout, 

 the distinctly annulated tail, the cleft upper lip, the moveable 

 muffle, and the ungulate digits. To expose the viscera, the 

 greater part of the right side of the abdomen and thorax has 

 been removed. A red injection has been thrown into the 

 arteries and veins. The general visceral cavity is divided by 

 the transverse tendino- muscular diaphragm into a thorax, 

 containing the heart and lungs, and an abdomen, in which the 

 liver, stomach, intestines, &c. are situated. The lungs are freely 

 suspended within a pleura! cavity, and are not closely adherent 



