l82d. 



HUMAN ANATOMY. 



surface of the epiglottis and the side and back walls of the larynx, its most usual 

 position being the ventricle (Fig. 1551). Within the laryngeal pouch the lymphoid 

 tissue is so constant and plentiful xXrAt laryngeal tonsil hdiS been suggested (^Fraenkel) 

 as an appropriate name for these collections. 



THE MUSCLES OF THE LARYNX. 



The extrinsic muscles of the larynx should include those going to the hyoid bone, 

 which is physiologically a part of this apparatus. These have been described in the 

 systematic consideration of the Muscular System (page 543). The intrinsic muscles 

 are the crico-thyroid, the posterior crico-arytejioid, the lateral crico-arytenoid, the thyro- 

 arytenoid, and the arytenoid. All of these, except the last, are in pairs. From a 

 physiological stand-point these muscles may be divided into three groups : the con- 

 strictors, including both the adductors of the cords and those which draw together the 

 supraglottic portion of the larynx ; the dilators, which abduct the cords ; and those 

 which viodify the tensiori of the cords without necessarily approximating or separating 

 them. The constrictors are the lateral crico-arytenoids, the thyro-arytenoids, and 

 the arytenoid. The dilators are the posterior crico-arytenoids. Those modifying 

 the tension of the cords are the crico-thyroids, which stretch them, and a part of 



the thyro-arytenoids, which relax 

 Tif''- 1553- them. Moreover, many of these 



muscles, even antagonistic ones, 

 when acting together may be con- 

 sidered as parts of a sphincter. 

 The laryngeal muscles are ex- 

 tremely variable, especially the 

 thyro-arytenoid, detached fibres 

 of which have been described as 

 the thyro-epiglottideus. 



The crico-thyroid muscle 

 (Fig. 1 5 10) is well defined, pass- 

 ing upward and outward from the 

 anterior ring of the cricoid to 

 the under border and the inferior 

 horns of the thyroid. The origiri 

 is from the whole of the anterior 

 surface of the arch, except for a 

 slight interval between the mus- 

 cles. I'he internal fibres are nearly 

 vertical and the lateral ones nearly 

 horizontal. The insertion is into 

 the lower border of the thyroid 

 cartilage from a point a few milli- 

 metres in front of the inferior tubercle to all the rest of the lower border and the front 

 of the inferior horn. It often extends a little onto the posterior surface of the ala. 

 The muscle is frequently divided into a superficial and a deep part. The distinction 

 may be very striking, or may be wanting. The superficial is the more internal 

 vertical part, which conceals a little of the origin of the deeper. The crico-thyroid 

 may be continuous by some fibres with the inferior constrictor of the pharynx. It 

 may descend to the first ring of the trachea, and it may give off fibres to the capsule 

 of the thyroid body. Occasionally the muscles of the two sides are connected at the 

 lower border of the cricoid. In extreme cases each may cross the median line. 



Actio7i. — This muscle is a tensor of the vocal cords by separating their points 

 of attachment on the thyroid cartilage from those on the arytenoids. Although the 

 conventional names of origin and insertion have been used, the more movable of the 

 two cartilages is the cricoid, and the action of the muscles is to raise its anterior arch, 

 thereby tipping the posterior plate with the arytenoids backward, and so stretching 

 the cords. While the thyroid can be held fixed by many muscles, the only extrinsic 

 one attached to the cricoid is a part of the inferior constrictor of the pharynx, so that 



Cartilage triticea 



Thyro-hyoid 

 membrane 



Aryepiglotticus 



Arytenoideus 

 oblique portion 



Arytenoideus, 

 transverse por- 

 tion 



Crico- 

 arytenoideus 

 posticus 



Epiglottis, dorsal surface 



Superior cornu 

 of hyoid bone 



Superior thyroid 

 cornu 



Cuneiform 

 tubercle 



Cartilage of 

 Satitorini 



Posterior margin 

 of thyroid car- 

 tilage 



Inferior thyroid 

 cornu 



Cricoid cartilage 



Trachea 



Muscles of larynx from behiiici. 



