I 



310 DISSECTION OF THE EABBIT 



4. The colon. 



Slit open part of the colon; wash; and examine under 

 u-ater, noting the papillose surface and the sacculations of the 

 wall. 



5. The rectum. 



Examine a part of the rectum in a similar manner, and 

 note its smooth mucous membrane. 



V. THE THOEACIC VISCEEA. 



Open the thorax by a transverse incision just in front of 

 the diaphragm : cut through the ribs along each side, and 

 remove the front wall of the thorax as a triangular piece, 

 taking great care not to injure the vessels and other structures 

 beneath it. 



Identify and examine the following parts without any 

 further dissection. 



1. The thymus is a pale, soft, glandular -looking body in the 



anterior part of the thorax. It is very variable in 

 size, being larger in the young animal, and some- 

 times extending back so as to overlap the heart. 



2. The heart, enclosed in the thin transparent pericardium, 



lies in the middle of the thorax : it is dark in colour 

 and conical in form ; the apex being directed back- 

 wards and slightly to the left ; and the base, with the 

 roots of the great vessels, forwards. 



3. The lungs are a pair of pink spongy bodies at the sides 



of the thorax, and filling the greater part of its 

 cavity. They collapse when the thorax is opened. 

 Find the trachea in the middle line of the neck, recognising 

 it by its transverse cartilaginous rings. Free it from the 

 surrounding parts about the middle of its course; make a 

 longitudinal incision in it; insert a blowpipe, and pass a 

 ligature loosely round the trachea behind it ; inflate the lungs 

 through the blowpipe, and when they are fully distended tie 

 the ligature firmly, so as to retain the air in the lungs. 



