166 Mr Houston on the Structure and Mechanism 



rounded and smooth, and about an inch and a half in length, and whose point, 

 when the mouth is closed, rests against the back part of the chin. The ante- 

 rior cornua (BB) are about three quarters of an inch long ; their outer extre- 

 mities, which are cartilaginous and pointed, are directed obliquely forwards. 

 Their inner extremities are articulated with the body of the bone, and a small 

 plate of cartilage stands out from each, which serves as a pully for one of the 

 muscles of the tongue, the hyoglossus. The posterior cornua (CC) are about 

 the same length, and slightly curved upwards. One end of each is attached 

 to the body by a moveable joint, the other passes round towards the back of 

 the occiput. 



The muscles are nine in number on each side. Three connect the os hyoi- 

 des to the thorax, the sterno-hyoid, the sterno-ceratoid, and the omo-hyoid. 

 Five extend from the os hyoides to the lower jaw, viz. the mylo-hyoid, ge- 

 nio-hyoid, together with three which may be called cerato-hyoid, and distin- 

 guished by the names external, middle, and internal. The ninth is a remark- 

 able muscle, the hyo-glossus. 



\st, The sterno-hyoid, (Fig. 2. a) a strong muscle, is attached by its posterior 

 extremity to the lower and back part of the sternum, and by its anterior one 

 to the body of the os hyoides. 



2rf, The sterno-ceratoid (b), at its origin from the sternum, is partly concealed 

 by that of the sterno-hyoid. It runs forwards and outwards, and is inserted 

 into the outer extremity of the posterior cornu of the os hyoides. 



3(f, The omo-hyoid (c) is long and slender, and interrupted about its centre 

 by a short tendon. It proceeds from the scapula to the middle of the os- 

 hyoides, passing in its course along the inner side of the sterno-ceratoid. 

 These three muscles serve the office of drawing back the os hyoides and 

 tongue. 



4/A, The mylo-hyoid* is a superficial muscle. It arises from the whole length 

 of the ramus of the lower jaw, and from the skin along side of the neck, and 

 running thence inwards, joins its fellow of the other side, underneath the os 

 hyoides. It supports the parts contained in the mouth and throat, while at 

 rest, and while performing the complicated actions of prehension and mastica- 

 tion of insects. 



Sth, The genio-hyoid consists of two parts ; one internal, slender (d), arises a 

 little to one side of the symphysis of the lower jaw, and is inserted into the 

 posterior part of the body of the os hyoides. The other (e) somewhat more 

 external, is larger and strocger, and inserted into the whole length of the pos- 

 terior cornu. A part of its external border bends inwards to be attached to 

 the anterior cornu. 



6th, The external cerato-maacillary (f ) arises from the posterior part of the 

 ramus of the lower jaw, and becoming broader, is inserted into the anterior 

 cornu of the os hyoides. 



Ith, The middle cerato-maxillary (g) is narrow, and in part concealed by the 

 external. It extends from near the centre of the ramus of the lower jaw 

 straight backwards, to be attached to the outer extremity of the posterior cor- 

 nu of the OS hyoides. 



* This muscle I have deemed it unnecessary to delineate. 1 have retained the name previous- 

 ly given to it, though I could not discover any attachment between It and the os hyoides. It might, 

 J think, be better named platisma myoides. 



