324 



VETERINARY PHYSIOLOGY 



Th 



many elastic fibres and are covered by a stratified squamous 



epithelium and appear white and shining. 



The vocal cords increase in length as the larynx grows, and 



in adult life they are generally longer in the male than in the 



female, and the whole larynx is larger. 



3. Muscles. The crico-lhyroids take origin from the antero- 



lateral aspects of the cricoid, and are inserted into the inferior 



part of the lateral aspect of 

 the thyroid. In contracting 

 they approximate the two 

 cartilages anteriorly, and 

 render tense the vocal cords 

 (fig. 146). 



The crico-arytenoidei postici 

 arise from the back of the 

 cricoid and pass outwards to 

 be inserted into the external 

 or muscular process of the 

 arytenoids. In contracting 

 they pull these processes in- 

 wards, and thus diverge the 

 anterior processes and open 

 the glottis (fig. 147). 



The crico-arytenoidei later- 

 ales take origin from the 

 lateral aspects of the cricoid, 

 and pass backwards to be 

 inserted into the muscular 

 processes of the arytenoids. 



Ar. 



FIG. 147. Cross Section of the Larynx, 

 to show the cricoid, Cr. ; thyroid, Th. 

 arytenoid cartilages, Ar. The con- 

 tinuous line shows the parts at rest, 

 the dotted line under the action of the 

 Lateral Crico-arytenoid Muscle, and 

 the dot-dash line under the action of 

 the Posterior Crico-arytenoid. 



They pull these forward and 

 so swing inwards their anterior processes and approximate 

 the vocal cords (fig. 147). 



A set of muscular fibres run between the arytenoids 

 the arytenoidei while others run from the arytenoids up to 

 the side of the epiglottis. These help to close the upper 

 orifice of the larynx. 



The thyro-arytenoid is a band of muscular fibres lying in 

 the vocal cords and running from the thyroid to the ary- 

 tenoids. Its mode of action is not fully understood. 



4. Mucous Membrane. The mucous membrane of the larynx 



