CHAPTER III. 



THE THORACIC VISCERA, BUCCAL CAV- 

 ITY, PHARYNX AND LARYNX. 



THE THORACIC VISCERA. 



Dissect off the skin and muscles from the thorax. 

 With tJie 'bone forceps cut carefully tJiroiLgh all the 

 bony ribs at a distance of several inches on each side of 

 the sternum. Remove the triangular piece of the 

 thoracic wall thus isolated. 



A. In removing this piece notice the vertical fold 

 of serous membrane passing from the heart 

 to the sternum ; it is a portion of the pleural 

 membrane known as the anterior mediastinum. 



1. The Thymus Gland lies in the anterior part of 

 the thorax anterior to the heart. It varies in size with 

 the age of the animal, being larger in the young and 

 decreasing in size as the animal grows older. 



2. The Lungs will be found collapsed when the 

 thorax is opened ; in the closed thorax they filled all 

 the space not occupied by the heart, great blood- 

 vessels, etc. They lie quite free in the cavity, except 

 at the roots, i.e., where the blood-vessels and bronchi 

 enter them. 



The left lung is divided into two lobes, the upper of 

 which is incompletely subdivided by a deep notch. 



