RESPIRATORY SYSTEM. 453 



divisions respectively. Their hinder borders 

 are attached by three sets of chordae tendinese 

 to muscular processes of the ventricular wall, 

 the musculi papillares. 



ii. The aperture of the aorta is at the anterior end 

 of the ventricle, and at its right side. In 

 the natural position it lies dorsal to the aper- 

 ture of the pulmonary artery. 



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

 it open with scissors along its right side. 



The semilunar valves are three pocket-like 

 flaps, similar to those of the pulmonary 

 artery. 



VI. DISSECTION OF THE RESPIRATORY 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 windpipe, 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 cartilaginous 

 dorsally. 



In the anterior part of the neck the trachea is 

 ventral to the oesophagus ; further back it lies along 

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

 ventral to the oesophagus, it divides into the two 

 bronchi, which run outwards and backwards to 

 enter the lungs on the ventral surface and near 

 their anterior ends. 



2. The lungs are a pair of spongy bodies, attached to the 



dorsal and dorso-lateral walls of the anterior part 

 of the thorax. They are covered ventrally by the 



