no PRACTICAL ANATOMY. 



to that of the other arytenoid cartilage. It approximates the vocal cords by 

 drawing the arytenoids together. 



The crico-arytenoideus lateralis (Fig. 72) arises from the upper border 

 of the side of the cricoid cartilage. It is inserted into the external angle of the 

 base of the arytenoid cartilage. The action is to draw the vocal cords together 

 and close the glottis. 



The crico-arytenoideus posticus arises on the posterior part of the cricoid. 

 It is inserted into the outer angle of the base of the arytenoid cartilage. This 

 muscle draws the vocal cords apart, and thereby opens the glottis. 



The crico-thyroid muscle arises from the side of the cricoid cartilage. It 

 is inserted into the lower corner of the thyroid cartilage. It tightens the vocal 

 cords. 



Describe the superior laryngeal nerve. (Fig. 71.) 



It is a branch of the ganglion of the trunk of the pneumogastric nerve. It 

 passes behind the internal and external carotid arteries. It is joined by com- 

 municating branches from the sympathetic nerve and the pharyngeal plexus. It 

 divides into an internal and an external branch. The external branch pierces the 

 inferior constrictor of the pharynx near the lower border of the thyroid cartilage 

 (Fig. 63), and is distributed principally to the crico-thyroid muscle ; some few 

 filaments are distributed to the mucous membrane. The internal division, in 

 company with the superior laryngeal artery, passes under the thyro-hyoid 

 muscle (Figs. 27 and 71), pierces the thyro-hyoid membrane, and is distributed 

 to the mucous membrane, communicating here with the recurrent laryngeal 

 nerve. (Fig. 71.) 



Describe the course of the recurrent laryngeal nerves. (Fig. 71.) 



The nerve of the right side is given off from the pneumogastric in front of 

 the first stage of the subclavian artery. It passes upward, under, and behind 

 the subclavian artery, then behind the common carotid to the side of the trachea. 

 It lies in a fatty groove between the trachea and oesophagus, and, in company 

 with the inferior laryngeal artery, passes upward, under the inferior constrictor 

 of the pharynx, to the larynx. It is distributed to all the intrinsic muscles of 

 the larynx except the crico-thyroid. The recurrent laryngeal nerve of the left 

 side is given off from the pneumogastric in front of the transverse part of the 

 aortic arch, passes under this vessel behind the obliterated ductus arteriosus, and 

 gains the fatty space between the trachea and oesophagus, and has the same sub- 

 sequent course and distribution as the nerve on the right side. In their course 

 between the oesophagus and trachea these nerves give off branches to these 

 conduits. 



Describe the blood-supply of the larynx. (Fig. 28.) 



The superior laryngeal artery is a branch of the superior thyroid. It accom- 

 panies the superior laryngeal nerve, piercing with this nerve the thyro-hyoid 

 membrane. The inferior laryngeal artery is a branch of the inferior thyroid. It 

 passes behind the inferior constrictor of the pharynx with its accompanying 

 nerves. 



Describe the trachea. 



It is an air conduit, extending from the larynx to the tracheal bifurcation, 

 where the bronchial tubes begin. Compared to the vertebral column, in front of 

 which the trachea lies, it extends from the fifth cervical to the fifth thoracic verte- 

 bra. It is one inch in width and five inches long. 



The structure of 'the trachea fits it admirably for its specific double function 

 (i) of transmitting air inward and (2) of extruding both air and accumulated 

 mucus, bearing crude inhaled impurities. Imperfect rings of cartilage, held 

 together by fibro-elastic membrane possessing some muscular fibres, a rich nerve- 

 ami blood-supply, and a lining of mucous membrane, are the anatomical tissues 



