PHARYNX AND LARYNX. 43 



go to two flaps, or one flap may have chordoc from 

 two papillary muscles. 



CiU through the right ventricular zvall between two 

 of the flaps to get a better view of their attachments. 

 Note the rcticnlated strnctiire of the ventricular 

 walls — the coiumnas carneae. 



b. The Pulmonary Artery. The portion of 

 the right ventricular cavity leading into the pulmonary 

 artery is known as the conus arteriosus and forms a 

 funnel-like recess. The opening into the artery is 

 guarded by three pocket-valves, the semi-lunar valves, 

 which can be exposed easily with a probe from the 

 opening of the artery above. Cut through the 

 conus and artery longitudinally to get a better view 

 of the valves. 



c. The Mitral Valve of the left ventricle 

 guards the left auriculo-ventricular orifice. It resem- 

 bles the tricuspid, with the exception that there are 

 only two flaps or cusps. 



d. The Aortic Semi-lunar Valves, three in 

 number, have the same structure as those of the pul- 

 monary artery. 



e. The Coronary Arteries. Behind two of 

 the aortic semi-lunar valves will be found the open- 

 ings of the two coronary arteries arising from the base 

 of the aorta. Run a probe into each and follow its 

 course for some distance. 



3. The Trachea and Bronchi. Find the trachea as 

 it enters the thorax. Dissect it toward the lungs. It 

 divides into two large branches, the bronchi, one for 

 each lung. If one of the bronchi is followed into the 

 lung to which it is distributed it will be found to give 

 off smaller bronchi at intervals, and these in turn give 

 off still smaller branches, the whole system forming 



