448 DISSECTION OF THE PIOEON. 



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 EESPIEATORY SYSTEM. 



Bemove 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 CESophagus, 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 pleura, 

 an anterior continuation of the peritoneum. Their 

 inner edges Ue close together, separated from each 

 other in the median plane by the projecting centra 

 of the thoracic vertebrre, and by the dorsal aorta. 



Remove the pleura from the ventral surface of one lung ; 

 and separate the lung from the thoracic wall, noting its close 

 attachment to this wall, and the grooves in its surface which 

 lodge the ribs. 



