60 LABORATORY WORK. 



enter? Where does the blood go from the left ventricle? 

 Insert a diagram of the heart, with its chambers, in the 

 sketch of the circulation. 



Between the common carotids is the ringed trachea, or 

 windpipe. Dissect it loose and cut near the head. Insert 

 a blow-pipe in the hinder portion and inflate the lungs by 

 blowing. Are the rings of the trachea complete? Trace 

 the trachea forward and notice enlarged anterior portion 

 (larynx), and just in front, and ventral to it, the hyoid 

 bone. Beneath the trachea (dorsal to it) is the oesophagus. 



Remove the skin from the head. Notice the large 

 muscles attached to the jaw, and just in front of the ear 

 the salivary (parotid) gland. Cut through the jaw muscles, 

 and, beginning at the angles of the mouth, carefully cut 

 backwards through the cheeks, so as to .allow the lower jaw 

 to be bent back. In the mouth-cavity study the teeth. 

 In front are the incisors, and further back the molars. 

 Notice the large gap (diastema) between them. How man}'- 

 of each kind in each jaw. With a knife test the hardness 

 of the front and back surfaces of the incisors. Which is 

 the harder? Why are these teeth always sharp? Is there 

 any such arrangement in the molars? 



Between the molars is the hard palate, its surface with 

 transverse folds. Farther back is the soft palate, bounded 

 behind by the place (internal narial opening) where the 

 nostrils communicate with the back part of the mouth- 

 cavity. How many of these openings do you find? Slit 

 soft palate with the scissors and see how this arrangement 

 is brought about. 



Opposite the internal narial opening (i.e., on the floor 

 of the pharyngeal region) is an opening the glottis, sur- 

 rounded by a raised rim, which is enlarged in front into 

 a soft epiglottis. Inside of the glottis may be seen two 



