76 STUDIES IN COMPARATIVE ANATOMY. 



springs from the basi-hyoid close to the middle line, and passes 

 directly backwards to the anterior surface of the epiglottis, 

 having a length of about three inches. The two muscles under- 

 lie the thyro-hyoid membrane and support this part of the floor 

 of the pharyngeal pouch. Camper's drawing (pi. xii. fig. 4) is 

 fairly correct, except that he does not indicate any separation of 

 the muscles of opposite sides. ' 



The upper or false vocal cord is rounded and hardly apparent 

 except behind. The lower is straight and well-defined, with a 

 sharp vibratile edge. A small laryngeal pouch leads backwards 

 from the ventricle, and extends for a short distance under cover 

 of the antero-external border of the arytsenoid cartilage. 



The superior laryngeal nerve pierces the anterior border of 

 the thyroid cartilage near its centre. 



Below the arytsenoid cartilages and vocal cords the internal 

 surface of the larynx is covered with longitudinally wrinkled 

 yellow elastic tissue similar to that of the trachea. The mucous 

 membrane above the vocal cords resembles that of the pharynx. 



Trachea. 



The trachea consists of about thirty rings. These are incom- 

 plete behind, and occasionally subdivided, the joints being 

 enclosed in synovial capsules. The tube is lined by yellow 

 elastic tissue thrown into firm and very narrow longitudinal 

 folds. The space between the ends of the rings behind is occu- 

 pied by two distinct layers of unstriped muscle, the outer layer 

 being transverse and the inner vertical in the central part, but 

 radiating outwards laterally. 



Bronchi. 



" The right bronchus consisted of eight, the left of six rings. 

 In addition to these, however, there were several cartilaginous 

 nodules of small size representing rudimentary rings. No 

 accessory bronchus, such as is so common among the ruminants, 

 was met with, the azygos lobe of the right lung receiving its air- 

 tube from the right bronchus after it had entered the substance 

 of the lung." — ( Watson.) 



