590 ANATOMY OF VERTEBRATES. 



surface for the arytenoid: the anterior part of the cricoid is convex 

 and notched above. Each arytenoid is an irregular three-sided 

 pyramid, the inner surface flat, the antero-external surface convex, 

 the postero-external surface concave, the base excavated to fit the 

 cricoid articular tubercle, with which it is articulated by a synovial 

 and fibrous capsule ; the apex is compressed and extended in the 

 antero-posterior direction, forming the convex lateral margin of the 

 glottis. The short space between the arytenoid and thyroid car- 

 tilages is traversed by a thick fasciculus of dense elastic fibres 

 representing the lower vocal cord, and covered by the lining 

 membrane of the larynx : there is a small pit between the ante- 

 rior insertions of the ' chordae/ but no other indication of sacculus. 

 The mucous membrane is smooth for a short extent below its 

 reflection and over the arytenoid apices, and then begins sud- 

 denly to be disposed in numerous narrow plica? which increase in 

 breadth as they descend into the trachea : at the back part of the 

 larynx are a few longitudinal rugae. There is no true cartilage 

 in the epiglottis : the small pyramidal prominence in front of the 

 glottis includes yellowish and white fibrous tissue which deo-eiie- 



o / o 



rates gradually into the areolar substance occupying the interalar 

 thyroid space : the other parts of the laryngeal framework have 

 bony granules scattered through their gristly tissue. A ' hyo- 

 epiglottideus' is continued from the fore part of the epiglottis to the 

 base of the tongue. The ' arytenoidei obliqui ' and ' transversi ' 

 are represented by a single pair of muscles, which derive a broad 

 and extensive origin from the posterior and external ridges of the 

 arytenoid cartilages, and converge to be inserted into a small round 

 cartilage in the posterior interspace of the arytenoids. These 

 muscles, through the advantage afforded them by this middle 

 fixed fulcrum (which ought therefore to be regarded as their 

 point of origin), act with great power upon the arytenoid carti- 

 lages, drawing them together, and thus forcibly closing the nar- 

 row glottis. They are directly opposed by strongly developed 

 6 thy reo- arytenoidei,' which pass obliquely backward from the 

 internal and interior part of each division of the thyroid cartilages 

 to the posterior and outer part of the arytenoids, which they 

 draw apart, and thus open the glottis. The ' crico-arytenoidei' 

 arise from the anterior border of the cricoid, and are so inserted 

 as to draw the arytenoidei forward as well as outward. The 

 6 crico-thyroidei ' cover the whole of the fore part of the cricoid 

 cartilage. The f sterno-thyroidei ' and ' thyreo-hyoidei ' are ex- 

 tremely powerful. 1 



1 cxvn". p. 32. 



