908 



THE ORGANS OF VOICE 



portion of the crico-thyroid meniljrano and some of the lower fibres of the 

 lateral crico-arytenoid muscle. The central portion of the crico-thyroid membrane 

 api)ears in the an<iular interval between the two muscles. 



The crico-arytenoideus posticus arises from the quadrate surface situated on 

 each side of the j)osteri{M- metUan ridge of the cricoid cartilage. Its fibres rajjidly 

 converge to be inserted into tlie posterior portion of the outer angle (muscular 

 process) of the arytenoid cartilage. 



Fig. 529.— Scheme of Kima, showing Action of Crico-aeytenoideus Posticis, which 

 DRAWS THE ARYTENOID CARTILAGE FROM I TO II. (Modified from Stirling.) 



The upper fibres are chiefly concerned in rotation of the arytenoid cartilage, 

 whilst the lower produce its gliding movement. It is a dilator of the rima glottidis. 



Some of the lowest fibres occasionally pass to the inferior cornu of the thyroid 

 cartilage, and are known as the kerato-cricoideus or kerato-thyroideus. 



It is covered posteriorly by mucous membrane, and is supplied by the recurrent 

 laryngeal nerve. A few of the longitudinal fibres of the oesophagus arise from 

 the ridge which separates the two muscles. 



Fig. 530. — Posterior View of Thyroid Cartilage with Epiglottis. 



GREATER CORNU OF HYOID 

 BONE 

 BODY OF HYOID BONE 



Thyro-hyoid ligament 



Median notch 



Origin of thyro-epiglottio 

 ligament 



POSTERIOR EDGE OF THYROID 



CARTILAGE 



Origin of thyro-aryte- 



noideus muscle 



INFERIOR CORNU 



SMALLER CORNU OF HYOID 

 BONE 



CARTILAGO TRITICEA 



SUPERIOR CORNU OF THYROID 

 CARTILAGE 



RIGHT ALA OF THYROID 

 CARTILAGE 



False vocal cord 

 True vocal cord 



Origin of thyro-epiglot- 

 tideus muscle 



The crico-arytenoideus lateralis arises from the uj>per border of the cricoid 

 cartilage between tlie origin of tlie crico-thyroid and the crico-arytenoid articulation. 

 It narrows to be inserted into the fore part of the muscular process of the aryte- 

 noid cartilage. It draws the cartilage forwards, relaxing and ap])roximating the 

 cords. 



It is overlapped l\y the thyroid cartilage, and anteriorly by the crico-thyroid 



