CHAP, vir.] SPECIAL MUSCULAR MECHANISMS. 311 



only of the front part of the slit from the thyroid to the processus 

 vocales ; from this point backwards, to the muscular and other 

 tissue which braces together the hind surfaces of the arytenoid 

 pyramids the slit is continued by the median edges of the bases 

 of the pyramids. Hence the whole slit consists of two parts : 

 of a front part from the thyroid (Fig. 185) to the processus 

 vocales, along which the edges are furnished by the membranous 

 vocal cords, and of a hind part from the end of the vocal cords back- 

 wards, the edges of which are not membranous but are furnished 

 by the bases of the arytenoids covered with mucous membrane. 

 The front part about 15 mm. long in the adult human male, is 

 sometimes called the " rima vocalis," and the hind part, about 

 8 mm. long, the " rima respiratoria ; " but these names are not 

 free from objection, and it is better to speak of the former as the 

 membranous or ligamentous and the latter as the cartilaginous 

 or inter-cartilaginous rima or glottis. 



The tubular passage of the trachea as it ascends within the 

 cricoid ring is narrowed funnelwise in a fairly uniform manner to 

 the slit of the rima glottidis ; but as we have already said the 

 larynx above the rima is less regular in shape. 



If the pharynx and oesophagus be laid open from behind (Fig. 

 182) or exposed in vertical section (Fig. 183) the " superior aper- 

 ture of the larynx " will be disclosed and will be seen to be oval or 

 roundly triangular in outline slanting downwards and backwards. 

 In front and high up the margin of the aperture is formed by the 

 projecting epiglottis (e). On each side the margin is continued 

 by a fold of mucous membrane (ar. e. /.) which passes obliquely 

 downwards and backwards from the base of the epiglottis, and 

 ends in the cartilage of Santorini and tip of the arytenoid of that 

 side. Each of these ary-epiglottic folds as they are called, just 

 before it reaches the cartilage of Santorini, is marked with a 

 rounded projection ( W} caused by the presence of a small nodule 

 of cartilage, the cartilage of Wrisberg. The cartilages of Santo- 

 rini also cause rounded projections (S), between which the mar- 

 gin of the upper aperture of the larynx is completed by a fold 

 of mucous membrane passing from the tip of one arytenoid to 

 that of the other ; this when the cartilages are dragged apart 

 is stretched straight but when they are drawn together is folded 

 into a notch (i). 



The cavity of the larynx into which this aperture thus slop- 

 ing rapidly backwards from the level of the epiglottis to that 

 of the tips of the arytenoids opens, does not narrow uniformly to 

 the glottis. A little above the true vocal cords (Figs. 183, 184 

 c.v.) the mucous membrane is thrown on each side into a some- 

 what thick transverse fold which, stretching from the base of the 

 epiglottis in front to the arytenoid behind, projects horizontally 

 inwards towards the middle line but does not reach so far as do 

 the vocal cords. These are called the ventricular bands or false 



