THORACIC VISCERA. 347 



IV. THE ABDOMINAL SYMPATHETIC GANGLIA. 



These are well seen in a fresh rabbit, especially in lean 

 specimens. There are two main ganglia, one, the c celiac, 

 in front of, and one, the anterior mesenteric, behind the 

 origin of the anterior mesenteric artery, at the level of the 

 left adrenal body. To see them, spread the viscera over to 

 the left side. A small additional ganglion occurs in relation 

 to the posterior mesenteric artery. 



V. THE THORACIC VISCERA. 



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 wall of the thorax as a tri- 

 angular 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. Each lung collapses as soon as the side of 

 the thorax on which it lies is opened. 



The lungs he 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 He across the median plane 

 behind the heart, and closely applied to the oesophagus. 



