238 



THE ANATOMY OF THE HORSE. 



lies between the bases of the arytenoid cartilages. The size of the 

 aperture is varied by the movements executed in the crico-arytenoid 

 joints, as already seen; and its form varies with its size. It can be 

 completely closed by the apposition of its margins in the mesial plane. 

 When it is only slightly opened it is a slit -like antero - posterior 

 aperture, widest at the centre ; when moderately open, as in easy 



respiration, it has the form of an elon- 

 gated isosceles triangle with the base 

 behind ; when dilated to the fullest 

 extent it is lozenge-shaped. 



The Ventricles, or Sinuses, of the 

 larynx. Each of these is a recess or 

 cavity, placed on the side of the larynx. 

 The entrance to it lies above the vocal 

 cord, whose free straight edge, covered 

 by mucous membrane, forms the lower 

 margin. The upper margin is formed 

 by a concave fold of mucous membrane, 

 containing in man a few fibres designated 

 the false vocal cord. The cavity of the 

 ventricle descends to the outer side of 

 the true vocal cord, and a pouch of the 

 mucous lining of the cavity passes out 

 between the upper and lower divisions 

 of the thyro-arytenoid muscle. 



The Sub-epiglottic Sinus is a depres- 

 sion beneath the base of the epiglottis, 

 and provided with a lunated fold of 

 mucous membrane. 



The Sub-arytenoid Sinus is a depres- 

 sion beneath the crico-arytenoid joints. 



Mucous Membrane of the Larynx. 

 This, which is continuous with the 

 lining of the pharynx and trachea, is of a pale yellowish-pink colour. 

 It forms the aryteno-epiglottic folds, and lines the ventricle of the 

 larynx. It is provided with numerous mucous glands. Its free 

 surface is covered by epithelium, which is ciliated except over the 

 vocal cords and around the superior aperture, in which positions it 

 is stratified and squamous. 



Fig. 33. 

 Interior of the Larynx, seen from 



BEHIND. 



1. Epiglottis ; 2. Arytenoid cartilage ; 

 2 1 . Its base where it bounds the glottis ; 

 3. Cut surface of cricoid cartilage ; 4. 

 Vocal cord ; 5. Ventricle of the larynx ; 

 6. Sub-epiglottic sinus. 



