THE SKULL 287 



already been described in connection with the 

 auditory capsule (p. 283). 



i. The squamosals are a pair of slightly curved 

 bony plates, which complete the side-walls 

 of the cranial cavity, lying in front of the 

 periotics, and articulating with the parietals, 

 frontals, orbito-sphenoids, and ali-sphenoids. 

 From the hinder border of each squamosal 

 a slender post-tympanic process arches back- 

 wards over the external auditory meatus, 

 lying along the outer surface of the periotic. 



From the outer surface of the squamosal 

 arises a stout zygomatic process, which bears 

 on its under surface the articular facet for 

 the mandible : beyond the facet it bends down- 

 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 deeplynotched : 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. 



