j8i4 



HUMAN ANATOMY. 



Fig. 



»S39- 



extremely variable in all its details. A median ridge divides the posterior stirface o\ 

 the cricoid cartilage into two symmetrical depressions for the origin of the posterior 

 crico-arytenoid muscles. Each lateral surface of the cricoid, below the middle, anfi 

 nearer the back than the front, bears an oval articular facet for the crico-thyroid 

 joint, its long diameter extending upward, backward, and inward. The facet, which 

 is nearly plane, faces chiefly outward, but also 

 somewhat upward and a little backward. The 

 long diameter is about 5 mm. and the cross one 

 nearly as great. A ridge connecting it with the 

 superior articular facet bounds the posterior sur- 

 face of the cartilage. The anterior surface of 

 the cricoid is somewhat convex vertically, so 

 as to resemble an over-large tracheal ring. 



The Thyroid Cartilage. — This, the 

 shield-shaped cartilage, consists of two quadri- 

 lateral plates, the alee, broader than high, which 

 meet in front and are widely apart behind. The 

 posterior border of each is prolonged upward 

 and downward into two horns, or cornua, some- 

 what flattened from side to side. The lower pair 

 rest on the inferior articular facets of the cricoid 

 and the upper are attached by ligaments to the 



ends of the greater horns of the hyoid bone. Being thus open behind, the thyroid 

 cartilage is complementary to the cricoid upon which it rests. The thyroid 7iotch 

 (incisura thyroidea) is a deep median depression of the upper border in front, extend- 

 ing nearly or quite half-way down. The plates are strongly everted (especially in 

 the male) at the sides of the notch, thus causing most of the prominence known as 

 Adam's apple { protuberantia laryngea). The resulting median ridge ends shortly 

 below the notch, and at the lower border the front of the thyroid is smooth and 

 convex. The upper border is slightly convex on either side, and usually presents a 

 small notch just in front of the root of each superior horn. The siiperior tubercle is 

 a little prominence on the outer surface, just below and anterior to this notch. The 

 lower border is alternately conyex and concave. There is a moderate median con- 

 vexity followed by a hollow, external to which is a marked prominence, the inferior 

 tubercle, between which and the inferior horn is a deep notch. The posterior border 



is slightly concave in the middle. 



Cartilage of Santorini, 



Posterior surface for 

 arytenoideus 



Posterior crico- 

 arytenoid ligament 



Muscular process 



Posterior ridge on 



cricoid cartilage 



Depression for 



crico-arytenoideus 



posticus 



Cricoid and arytenoid cui Ulages from behind. 



Fig. 1540. 



The oblique line is a ridge running 



Epiglottis 



Superior 

 cornu 



downward and forward from the 

 upper tubercle to the lower. It 

 marks the interruption of the mus- 

 cular layer out of which the sterno- 

 thyroid and the thyro-hyoid mus- 

 cles arise. The inferior constrictor 

 of the pharynx is inserted behind it. 

 The superior horns, usually longer 

 and more flexible than the inferior, 

 run upward, backward, and inward. 

 They become more cylindrical and 

 have blunt rounded ends. The in- 

 ferior horns, broader than thick, 

 run downward and slightly inward, 

 with a turn forward at the ends. In- 

 ternally each presents near the tip 

 a round articular surface of indefi- 

 nite shape" for the inferior articular surface of the cricoid. The dimensions of the alae 

 vary with the sex : in man the height is 30 mm. and the breadth 38 mm. ; in woman, 

 23 and 28 mm. respectively. The prominence and sharpness of the angle are male 

 characteristics, in man the average being 90° and in woman 120°. It is chiefly 

 through the thyroid cartilage that the male larynx acquires its relatively large size. 



Oblique line, end- 

 ing in tubercles 

 above and below 



Projection, be- 

 low notch, 

 forming po- 

 mum Adami 



Inferior cornu.. 

 Thyroid cartilage, with epiglottis, right antero-lateral aspect. 



