THE LARYNX 



907 



The crico-arytenoid joints possess a synovial membrane enveloped in a thin 

 and moderately loose capsule, strenfi;thened posteriorly by a band ])assino: Ix'twccn 

 the cricoid and the inner and back jjart of the arytenoid — the posterior crico- 

 arytenoid ligament; and internally by tlic intcrarytenoid band, which is occa- 

 sionally lijianicntoiis — the crico-arytenoid ligament. 



The cricoid articular surface is oval, convex, and oblique, Avith its long axis 

 passing from behind, forwards, and outwards. The opposed articular surface on 

 the base of the arytenoid is also oval, but it is concave with its long axis passing 

 from before backwards. 



It follows that the two surfaces never completely cover each other at any one 

 time. The arytenoid rotates on a vertical axis near to and parallel with its inner 

 surface, and it also glides forwards and inAvards, or in an opjoosite direction. 

 Tbese movements are associated — the gliding forwards and inwards with the inward 

 rotation, and the gliding outwards and l)ackwards with the outward rotation. 



Fig. 528.— Side View of the Muscles and Ligaments of the Larynx. 



Epiglottis — 



Cut edge of hyo-epiglottidean 

 ligament 



SECTION THROUGH BODY OF HYOID 

 BONE 



Periglottis 



Cut edge of thyro-hyoid 

 membrane 



ihyro-epiglottideus muscle 



SECTION OF THYROID CARTILAGE 

 Thyro-arytenoideus muscle 



Crico - arytenoideus lateralis 

 muscle I the pointer crosses 

 crico-thyroid membrane) 



CRICOID CARTILAGE 



Aryteno-epiglottidean fold 

 Aryteno-epiglottideus muscle 



Arytenoideus muscle 



Crico-arytenoideus posticus 



Heeurrent laryngeal nerve 



IWIII'" w W*""' 1'' 



The Muscles. — The muscles are divisible into an extrinsic group, passing 

 between the larynx and parts beyond; and an intrinsic group, belonging entirely to 

 the organ itself. 



The extrinsic muscles are the sterno-thyroid, thyro-hyoid, stylo- and palato- 

 pharyngei, and the inferior constrictors of the pharynx. It should be noted that 

 tb.e muscles whicli fix the hyoid bone, and also those which close the loAver jaw, 

 assist the action of the above mentioned. 



The intrinsic muscles. — The crico-thyroid is attached lielow to the front and 

 side of tbc cricoid cartilage, and nl)ove to the lower border of the thyroid cartilage. 

 The loAver fibres, which are horizontal and often distinct, pass to tbe front ))order 

 of its inferior cornu, and act by i)ulling the cricoid directly backwanls, whilst the 

 s])reading fi])res whicli form the rest of the muscle swing tlie cricoid l)etween the 

 crico-thyroid joints, pulling it upwards as well as backwards. Both portions of the 

 muscle make tense the vocal cords, and are su]>pned by the external laryngeal 

 nerve. It is overlapped laterally by the sterno-thyroid, having beneath it a small 



