NORMAL ANATOMY OF THE LARYNX. 



101 



number,* of which three are single and un- 

 symmetrical, the epiglottis, thyroid, and cri- 

 coid ; two are placed laterally, and form a pair, 

 called the arytenoids. Upon the summits 

 of these are found two minute cartilaginous 

 bodies, termed cornicula ; the remaining 

 two (which, however, are not always present) 

 are situated anterior to the arytenoids, and in- 

 volved in the aryteno-epiglottic folds, named 

 the cuneiform cartilages. 



The cricoid cartilage. Gr. x^ixo?, a ring, 

 &>?; Lat. Cartilugo anmdiformis ; Fr. Cri- 

 coide on unnulaire ; Germ. Ringknorpel ; Ital. 

 Cricoide. This cartilage, situated at the base 

 of the larynx, which it supports, is the thickest 

 and strongest of the whole assemblage of car- 

 tilages. It is connected to the first ring of the 

 trachea by elastic ligaments and mucous mem- 

 brane. Its form, that of a ring, is not quite 

 circular, but approaching to an elliptical figure. 

 It is shallow in front, at c, e, (fig.%0,) but it 

 is thicker and deeper than the first ring of the 

 trachea; and, posteriorly, it is considerably 

 deeper than at its anterior part, in the propor- 

 tion of eight to two and a-half. 



Fig. 20. 



A B 



A, an anterior, B, the side view of the cricoid 

 cartilage ; a, the posterior superior margin -, b, b, 

 the crico-arylenoid articulating surface; b,g,f,e, 

 the superior descending margin ; d, e, the trachea! 

 aperture of the cricoid ; a, d, the greatest, a, e, the 

 least depth of surface ; a, e, the obliquity of the 

 superior section to the axis ; h, the left surface 

 articulating with the inferior cornua of the thyroid 

 cartilage. 



The anterior external surface gives attach- 

 ment to the crico-thyroid muscles (see Jig. 26); 

 more posteriorly we find an apophysis for the 

 articulation of the thyroid (h,Jig. 20, B). Its 

 posterior surface is divided into two equal por- 

 tions by a vertical ridge along its middle line, 

 a, d, Jig. 20, B. This ridge, which was first 

 noticed by Galen, gives attachment to some 

 longitudinal fibres of the oesophagus. On each 

 side of it a concave surface is observed, which 

 gives origin to the crico-arytenoidei postici, 

 e, e,fig. 27. 



The internal surface is smooth, and lined by 

 the mucous membrane of the larynx. The 

 inferior margin is horizontal, and nearly circu- 



* Galen describes only three, j^ovJpo? 6wsosi$>)?, 



lar; but the superior, which is bevelled 

 obliquely inwards and upwards, about c, e, 

 (fig- 20,) ascends backwards in the direction 

 ofe,f,g, b, (Jig. 20,) being slightly curved 

 downwards between Jf and g. The anterior 

 superior outline of this cartilage presents that 

 of the section of a cylinder, whose obliquity to 

 its axis is in the direction , e, and therefore is 

 elliptical. It recedes anteriorly from the lower 

 margin of the thyroid cartilage in the direction 

 of g,f, e, (fig. 20,) leaving an interval called 

 the crico-thyroid space, a, (fg.W, B,) which is 

 occupied by the crico-thyroid ligament ; on each 

 side, in the lines e, f, g, by the lateral liga- 

 ments, and more posteriorly by the crico- 

 arytenoidei laterales, in the space,/", g, to the 

 external side of b (fig. 20). 



The posterior superior margin is horizontal 

 on each side of a, (fig. 20,) and parallel to the 

 inferior at d, having at b and b an oblong, 

 oblique, and slightly cylindrical surface, in- 

 clined upwards and outwards for the articu- 

 lation of the arytenoid cartilages. These sur- 

 faces are considered by Willis as " portions of 

 cylinders, whose axes are inclined both with 

 respect to the horizontal and vertical sections." 

 In the vertical section, the projection of this 

 articulating axis is in the position G, C, (fig. 

 28,) and in the horizontal, in the line O, P, 

 (fig. 30.) Between these surfaces is a slight 

 depression for the insertion of the arytenoid 

 muscles. 



The thyroid cartilage. Syn. Lat. Cartilago 

 scutiformis ; Fr. Thyroids; Germ.Schildknor- 

 pel. This cartilage derives its name from flt/gsof, 

 a shield, and &;, form. It embraces the 

 cricoid in a manner analogous to the carapax 

 of the tortoise. It is formed to protect the 

 internal mechanism of the larynx, both in front 

 and at both sides, but is open behind. It serves 



Fig. 21. 



An angular view of the thyroid cartilage, a, the 

 notch ; b, b, the superior cornua ; c,c, the inferior 

 cornua ; g, g, the superior tubercles ; h, h, the in- 

 ferior tubercles; e, e, the wings of the thyroid ; 

 i, a, i, the superior margin ; h, d, h, the inferior 

 margin ; a, d, the mesial line ; f t the pomum. 



as a fulcrum and lever for the action of several 

 muscles. It is composed of two quadrilateral 

 lamina; uniting in front at the mesial line (a, d, 



