THOEACIC VISCEEA. 337 



4. The colon. 



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

 water, rioting 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. 



IV. THE THOEACIC VISCEEA. 



Open the thorax by a transverse incision just in front of 

 the diaphragm : cut through all the ribs except the first along 

 each side, and remove the ventral luall of the thorax as a tri- 

 angular piece, tahiivg great care not to injure the vessels and 

 other structures beneath it. 



Identify and examine the following parts without any 

 fv/rpfier dissection. 



L/\. 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. Each lung collapses as soon as the side of 

 the thorax on which it hes is opened. 



The lungs lie quite free in the thoracic cavity, 

 except at their roots, where the blood-vessels and 

 bronchi enter them. The left lung is divided into 

 two lobes; and the right into four, of which the 

 smallest and hindmost lies across the median 



z 



