406 DISSECTION OF THE PIGEON 



i. The left auriculo-ventricular or mitral valve is 

 formed by two membranous flaps, which 

 hang into the ventricle. Their lower borders 

 are attached by chordae tendinese to muscular 

 processes of the ventricular wall, the mus- 

 culi papillares. 



ii. The aperture of the aorta is at the anterior 

 end of the ventricle, and at its right side. 

 In the natural position of the parts, it lies 

 dorsal to the aperture of the pulmonary 

 artery. 



Pass a seeker from the ventricle along the aorta, and lay 

 it open with scissors along its right side. 



a. The semilunar valves are three pocket-like 

 flaps, similar to those of the pulmonary 

 artery. 



VI. DISSECTION OF THE BESPIEATOBY SYSTEM. 



Remove the heart, if this has not already been done, and 

 also the alimentary canal and liver. Clean the trachea and 

 the ventral surface of the lungs. 



1. The trachea, or wind-pipe, is a tube which commences 

 in front at the glottis, runs back along the neck, and 

 divides in the thorax into two bronchi, entering the 

 right and left lungs respectively. 



It is surrounded by a series of closely set rings, 



which are ossified ventrally, and cartilagiiious along 



the dorsal surface. ■ • 



■ ' '-■ In the anterior part of the neck .the trachea is 



-. -.-...:^:ventral.to the gesoph'aguB.7 -further back -it lies along 



its left side. In the .thorax, where -it again lies 



- . -:. 77 ventral to'the--(]esaphagus,. it divides., into;the two 



-J bronchi,^ which run outwards and .backwards to enter 



the lungs on their ventral surface and near their 



anterior ends. 



