THE SKULL. 23 



cartilaginous cap, whose hollow is continuous with the 

 tympanic cavity. In front, the squamosal articulates 

 with the quadrato-jugal and the quadrate ; and, behind, 

 it overlaps and conceals parts of the quadrate and opis- 

 thotic bones. 



36. The quadrate forms a large, irregular, bony mass, 

 in which lies much of the tympanic cavity. It is pro- 

 duced ventrally to articulate with the mandible. It 

 articulates at its upper end, on the inner side, with the 

 prootic and opisthotic bones. In removing the quad- 

 rate, take care not to displace the columella auris. 



37. The o;pisthotic, which protects the posterior part 

 of the inner ear, may now be removed and examined ; 

 it forms the posterior boundary of the fenestra ovalis 

 (26, d). Behind, it articulates with the exoccipital ; 



> above, with the supra-occipital ; and in front with the 

 prootic. It also articulates with the quadrate, which 

 conceals a great portion of it in the natural positions of 

 the parts. 



38. In front of the opisthotic is the prootic, bound- 

 ing the fenestra ovalis in front. It articulates with the 

 last bone ; also in the base of the skull with the basi- 

 sphenoid and pterygoid ; and above with the parietal 

 and epiotic. 



39. The epiotic lies above the prootic and opisthotic, 

 with both of which it articulates. In adults it is not 

 separable from the supra-occipital. 



40. The supra-occipital bone bounds the foramen mag- 

 num above ; in front it is overlapped by the parietals ; 



