THE SKULL 279 



wards, to articulate by an expanded end with 

 the jugal bone, and so complete the zygomatic 

 arch. 



ii. The mandible, or lower jaw, consists of a pair of 

 somewhat triangular plates of bone, firmly 

 united together in front, and articulating by 

 their posterior and upper angles with the 

 zygomatic processes of the squamosals. 



The anterior portion of each half or ramus 

 is stout ; it lodges an incisor tooth in front, 

 and further back, on its upper margin, the 

 grinding teeth. The hinder part of the ramus 

 is much thinner : its postero-inferior border, 

 or angle, is rounded, and inflected along its 

 margin : its posterior border, above the angle, 

 is deeply notched : its upper border is thickened 

 to form the longitudinally elongated condyle, 

 which articulates with the squamosal in such 

 a way as to allow free movement of the jaw 

 backwards and forwards, but very restricted 

 movement from side to side : its anterior 

 border is deeply grooved, the outer lip or 

 coronoid process being inflected. 



On the inner surface of each ramus, just 

 behind the grinding teeth, is the inferior 

 dental foramen, through which the mandi- 

 bular nerve enters to supply the teeth. 



The hyoid bone lies in the floor of the hinder part of 

 the mouth, between the rami of the mandible. 



It consists of a median body, and two pairs of 

 backwardly projecting cornua, of which the posterior 

 are the larger. 



The anterior cornua are the ventral ends of the 

 hyoidean arches, the dorsal ends of which are 

 probably represented by the stapes : the posterior 

 cornua are the lower ends, and only persistent parts, 

 of the first pair of branchial arches. 



