THE HEAD AND NECK 



1289 



lages, and so the rima glottidis is closed. The lateral crico-arytenoid 

 muscle is covered externally by the ala of the thjToid cartilage 

 and the upper fibres of the crico-thyroid muscle, and internally by 

 the lateral expanded portion of the crico-thjToid membrane. 



Epiglottis 



Left Ala of Thyroid. 

 Cartilage 



Arytaenoideus. 

 Muscular Process. 



Crico-arytaenoideu s . 

 Posticus 



^-Hyoid Bone Qd secticm) 



!^.«TbyTO-arytaeno-epigk>ttidetis 



.Ala of Thyroid Cartilage 



(in section) 

 Thyro-arytaenoideus 



— Crico-arytienoideus 

 Lateralis 



Ciic(»d Cartilage 



Fig. 536. — The Intrinsic Muscles of the Larynx (Lateral View). 

 (The greater part of the Right Ala of the Thjroid Cartilage has been removed) 



Thyro-arytenoid. — This muscle consists of two portions, external 

 and internal. 



External Portion — Origin. — (i) The lower half of the inner 

 surface of the ala of the thyroid cartilage, and (2) the outer surface 

 of the lateral portion of the crico-thyroid membrane. 



Insertion — ^The front of the muscular process and the adjacent 

 part of the outer border of the arytenoid cartilage, a few of the 

 fibres passing round the cartilage to become continuous with the 

 arytaenoideus. The uppermost fibres of this portion pass upwards 

 and backwards to the aryteno-epiglottidean fold, and thence to 

 the epiglottis, under the name of the thyro-epiglottideus. 



Internal Portion — Origin. — (i) The receding angle of the thyroid 

 cartilage, and (2) the cartilage of Luschka in the anterior part of 

 the true vocal cord. According to Ludwig the deepest fibres of 

 this portion, known as the ary-vocalis, spring from the anterior 

 part of the true vocal cord. 



Insertion. — ^The outer surface of the vocal process of the arytenoid 

 cartilage, and the adjacent portion of the antero-extemal surface. 



The fibres pass from before backwards, some of them having a 

 slight inclination outwards, and the highest backwards. 



