44 THE FROG 



to the root of the lung of that side, taking care not to injure 

 the lung. Continue this cut forward through the floor of 

 the mouth close to the jaw to a short distance in front of the 

 hyoid apparatus ; make a transverse cut here and a cut similar 

 to the first down the other side of the oesophagus. Remove 

 the piece cut out and place it, ventral surface up, in a dish of 

 water. Taking care not to injure the thyroid glands (see 

 Section IX), clear away the muscles in case this has not 

 already been done completely, and observe the larynx em- 

 braced by the thyrohyoid process of the hyoid. The skeleton 

 of the larynx is composed of the cricoid and the arytenoid 

 cartilages. The cricoid cartilage consists of a slender ring 

 surrounding the larynx and lying in nearly the same plane 

 as the thyrohyoid process, to which it is closely attached; at 

 its posterior end it is produced into a median process or 

 spine. From near its middle the cricoid cartilage gives rise 

 to a transverse ventral loop, the tracheal process, which 

 serves as a means of attachment for the lungs. The aryte- 

 noid cartilages are a pair of semi-lunar valves, whose ap- 

 posed edges form the lips of the glottis; they afford attach- 

 ment to muscles by which the glottis may be opened and 

 closed. 



Cut through the transparent membranous ventral wall of 

 the larynx and expose the interior. Observe the vocal 

 cords, two strong membranes attached to the anterior and 

 posterior walls of the larynx; the inner edges are free and 

 may be set in vibration by the expulsion of air from the 

 lungs, thus producing the frog's peculiar croaking sound. 

 The vocal apparatus of the male is larger than that of the 

 female. 



Cut open one of the lungs by a longitudinal incision, pin it 



