in.] THE CRANIAL SKELETON. 9 t 



When the skull is divided vertically and in the direction 

 of the sagittal suture, we may note the vast size of the brain 

 cavity in proportion to the face ; also the horizontal con- 

 dition of the cribriform plate and foramen magnum, and the 

 advanced position of the latter approaching the middle line 

 from behind forwards. 



The basilar parts of the occipital and sphenoid bones are 

 seen to become rapidly thicker as \ve go forwards ; they form 



FIG. 91. VERTICAL, LONGITUDINAL SECTION OF MAN'S SKULL. 



a, greater wing of the sphenoid ; an, meatus auditorius interims ; bo, body of the 

 occipital bone ; bs, body of the sphenoid ; c, condyle ; c ', crista galli ; cy, con- 

 dyloid foramen ;_/", frontal ; me, median ethmoid ; mx, palatine plate of the 

 maxillary ; n, nasal ; o, squama of the occipital bone ; /, parietal ; //, palatine 

 bone ; pt, internal pterygoid process ; s, frontal sinus ; sq, squamous part of 

 temporal bone (beneath it is the petrous part of that bone, with the opening 

 an) ; t, lowest turbinal bone ; v, vomer. The straight line passing upwards 

 and forwards from the hinder end of the body of the occipital bone, represents 

 the basi-cranial axis. The line passing downwards to the front of the jaw, 

 represents the basi-facial axis. 



the true axis of the skull, and a line drawn from the anterior 

 margin of the foramen magnum to the front end of the 

 middle part of the upper (or cerebral) surface of the sphenoid 

 is called the basi-cranial axis. A line drawn from the same 

 point of the sphenoid plate to the front part of the alveolar 

 margin of the maxilla is the basi-facial axis, anjfl the two 

 axes in man form an angle which varies from 90 to 120. 

 The basi-cranial axis forms with the foramen magnum a 



