v///: HEAD. 



r>3 



inferior incisors, and behind these, in male animals only, there is an 

 additional alveolus for the tusk. The portion included on each side between 

 the last incisor and first molar, forms a more or less sharp ridge, which 

 constitutes thi! inferior interdental space or bars. 



Structure and development. Formed, like all the flat bones, by two 

 compact plates separated by spongy tissue, the inferior maxilla is developed 

 from two centres of ossification, which correspond to each branch, and which 



!esce some time after birth. 



11. The Hyoid Bone. 



The hyoid bone constitutes a small and special bony apparatus which 

 B to support the tongue, as well as the larynx and pharynx; its 

 description is placed immediately after that of the bones of the head 

 because of its connection with that region, it being situated between the two 

 branches of the supermaxillary bone, and suspended to the base of the cra- 

 nium in an oblique direction from above to below, and from before to behind. 



This apparatus is composed of seven distinct pieces, arranged in three 

 - : a middle, constituted by a single bone, and named the body ; two 

 lateral, forming two quasi-parallel branches, to the extremities of which the 

 body is articulated. 



Body. The body of the hyoid resembles a fork with two prongs. It 

 presents: 1, A middle part flattened above and below, and consequently pro- 

 vided with a superior and an 

 inferior face ; 2, A single and 

 long prolongation flattened 

 on both sides, which is de- 

 tached from the middle part, 

 and directed forward and 

 downward to plunge into the 

 muscular tissue of the 



tongue: this is the anterior ]ivoiii noN|; 



appendtxoj the hyoideal body ; 1? lt Superior evtl ,. n , itv , thu stvl(lill u , nes . o, Angle 



.I. i\OO lateral COntUO, tkyrotd described by their posterior border; 3, 3, Styloi.l 



Cornua, OF great cornua, pro- bones; 4,4, Extremities of the thyroid cornua; 5, 



jecting backwards and up- Articular surface of the body corresponding with the 



wards, articulating by their ^all branches; , Anterk ,,pp,ndix of the M 71 



' .,. f, . , 7, 7, Small branches, or styloid cornua. 



extremities with the thyroid 



cartilage of the larynx, and offering, at their point of union with the 

 middle part, two convex diarthrodial facets looking upwards, and corre- 

 sponding with the stylnid cornua. The body of the hyoid bone is developed 

 by three centres of ossification, a middle, and two lateral for the coruua. 



'i-hes. The three pieces composing these are articulated end to 

 -nd, by means of a cartilaginous substance that joins them together; they 

 are of very unequal dimensions. The first, which is in relation with the 

 body, is of medium size, and is named the xtyloid cornu, small cornu, or tamll 

 bi-iini-li. The second, termed the xti/!i<l nuclriix, is the smallest. The third, 

 the largest, constitutes the xhjlaiil /</-'vsx, or lunu', or </rtt lirnm-lt. 



1. The xti/li.iil rurnu is a small cylindrical piece bearing a concave 

 diarthrodial surf arc on its inferior extremity to unite it to the body ; it is 

 very spongy, and in developed from two ossifying centres, one of which, the 

 epiphysary, is for the inferior extremity. 



2. The xtylolil nucleus, which is often absent, is imbedded in the uniting 

 laginous substanc- . 



