344 HEAD AND NECK 



the corresponding surface of the opposite cartilage, from which 

 it is separated by the rima glottidis ; another looks back- 

 wards ; whilst the third is directed antero-laterally. The 

 medial surface is narrow, vertical and even, and is clothed 

 with mucous membrane. The posterior surface is concave ; it 

 lodges and gives attachment to the arytaenoideus transversus 

 muscle. The antero-lateral surface is the most extensive of 

 the three, and is uneven for muscular and ligamentous attach- 

 ments. Upon that aspect of the arytaenoid cartilage the 

 musculus vocalis and the thyreo- arytsenoid muscle are in- 

 serted. The surfaces of the arytaenoid cartilage are separated 

 by three borders, viz., an anterior, a posterior, and a lateral. 

 The lateral border is the longest, and, at the base of the 

 cartilage, it bulges backwards and laterally in the form of a 

 stout, prominent angle or process, termed \he processus muscu- 

 laris. It gives attachment, anteriorly, to the crico-arytaenoideus 

 lateralis muscle ; and, posteriorly, to the crico-arytaenoideus 

 posterior. The anterior border of the arytaenoid cartilage is 

 prolonged into the projecting anterior angle of the base, 

 which is called the processus vocalis. The vocal process is 

 sharp and pointed, and gives attachment to the vocal ligament 

 (O.T. true vocal cord). The base of the arytaenoid cartilage 

 presents an elongated concave facet, on its under aspect, for 

 articulation with the upper border of the lamina of the cricoid 

 cartilage. 



Crico-arytaenoid Joints. The crico-arytaenoid joints are of 

 the diarthrodial variety. Each has a distinct joint cavity, sur- 

 rounded by an articular capsule, which is lined with a synovial 

 stratum. The cricoid articular surface is convex ; that of the 

 arytaenoid is concave ; both are elongated in form, but they 

 are placed in relation to each other so that the long axis of 

 the one intersects or crosses that of the other, and in no 

 position of the joint do the two surfaces accurately coincide. 

 The movements allowed at the joints, as the dissector can 

 readily determine, are of a twofold kind (i) gliding, by 

 which the arytaenoid is carried medially or laterally, or, in 

 other words, a movement by which the arytaenoid advances 

 towards or retreats from its fellow; (2) rotatory, by which the 

 arytaenoid cartilage rotates round a vertical axis. By that 

 movement the vocal process is swung laterally or medially, so 

 as to open or close the rima glottidis. 



The dissector should note that the capsule of each joint 



