ARTICULATIONS Of mi' in: AD. i::w 



described here. Lad rl in<>r<'nn'nlx take placo when the inferior extremity of 

 tlu: j:i\v is curried alternately to tho right and left. It then happens that 

 i me of the maxillary condyles, taking with it the fibro-eartilago, is brought 

 into contact with the temporal condyle, while tho other is imbedded in tho 

 glonoid cavity of the opposite side. The horizontal <jli<lin<j is effected from 

 In hind to before, or vice versa. In tho first case, the two maxillary condyles 

 are carried at the same time under tho temporal condyles, bearing with 

 thrm tho lihro-cartiluges. In- the second case, they are drawn into the 

 ,L r l< noiil cavities, and rest against tho supracondyloid eminence, which 

 ]>n vents their going further. It will bo understood, after this brief 

 description, that the presence of the fibro-cartilages singularly favours tho 

 Literal movements and horizontal gliding of the lower jaw. 



In the l'i<j tin- t< mporo-maxillary articulation is formed after the same type as that 

 : nts. and allo.v.s very extrusive movements from before to behind; a circumstance 

 dii'- tn the complete- absence of the. supracoiidyloid eminence. 



In the Hoy and ('// the maxillary condyle is exactly fitted into the temporal cavity. 

 This dit>i>ositioii, in giving great precision to the movements of depression and elevation, 

 ivsiiains in a sinirular manner the lateral and horizontal gliding motions.. The inter- 

 art icnlar libro-eartiluge id extremely thin in these animals. 



5. Hyoideal Articulations. 



(I'l-i punitiiiii. Disarticulate tho lower jaw, and dissect away from the right of each 

 'datiou the muscles that may conceal the view.) 



These arc of two kinds : extrinsic and intrinsic. The first comprise tho 

 two tetiporokyoidetd articulations; to tho second belong the joints which 

 nnito the different pieces of the hyoid bone the interkyoideal articulations. 



TKMPORO-HYOIDEAL ARTICULATIONS. These are two amphiarthrodial 

 joints, in the formation of which each great branch of the hyoid bouo 

 opposes its upper extremity to the hyoideal prolongation lodged in tho 

 vaginal sheath of the temporal bone. An elastic cartilage, from 4-lOths to 

 6-lOths of an inch in length, unites the two bones in a solid manner ; and 

 it is owing to the flexibility of this cartilage that the hyoid bone can movo 

 entirely on the temporal bones. 



INTEUHYOIDKAL ARTICULATIONS. A. The great branch articulates with 

 the small one by an amphiarthrosis analogous to tho preceding. To form 

 this articulation, these two pieces of bone arc joined at an acute anglo 

 through the medium of a more or less thick cartilaginous band, in tho 

 centre of which there is often a littlo bony nucleus. This cartilage is elastic 

 and flexible, and permits the opening and closing of tho articular angle at 

 the summit of which it is placed. 



J5. Each small branch is united to tho body of tho hyoid bone by an 

 arthrodial articulation. Tho articular surfaces are : for tho hyoideal branch, 

 the small cavity terminating its inferior extremity; for the hotly, the 

 rounded lateral facet situated at the origin of the cornn. These surfaces 

 are covered by cartilage, and enveloped by a small synovial sac and a 

 peripheral fibrous capsule. They can glide on each other in nearly every 

 direction. (Median and superior hyoideal capsular ligaments are described 

 by Leyh as sometimes present. Tho latter unites tho upper and middle 

 l.r.nieli. g, and the former tho middle with tho inferior hranehes. They ore 

 absent when these branches are confounded with tho superior ones.) 



