120 



BONES OF THE SKULL. 



Fig - 87 - 



Internal surface. 



Fig. 88. 



14. 



Figs. 88 and 89 represent the anterior and posterior surfaces 

 of the petrous portion of the temporal bone in which the in- 

 ternal ear is situated. These 

 parts, consisting of the tym- 

 panum and its ossicles, the 

 labyrinth with the vestibule, 

 semicircular canals, and coch- 

 lea, have been already de- 

 scribed in our section on the 

 internal ear. 150 to 154. 



[ 245. Fig. 90 shews the 

 external surface of the occi- 

 pital bone (os occ^zYz's), with 

 its arched protuberances (10), 

 for giving attachment to the 

 muscles of the neck, and 

 the large aperture (foramen 

 magnum) (13) serving for 

 the passage of the spinal 

 cord. The basal portion is 

 seen at (14) ; at each side of 

 the foramen magnum are seen 

 the condyles (16, 16), by 

 which the skull rests upon 

 the first vertebra of the neck, 

 and moves backwards and for- 

 wards thereon. 



Fig. 90* represents the in- 

 ternal surface of the os occi- 

 pitis, which behind the fora- 

 men magnum (13), is divided 

 into four cavities by a crucial 

 ridge (23, 23,24, 24). To the 

 vertical spine, above the trans- 

 verse portion, is attached the 

 falx cerebri, and to that below, 

 the falx cerebelli, whilst to the 



transverse ridge the tentorium is attached : the cavities above 

 the transverse spine (21, 21) are for lodging the posterior 

 lobes of the cerebrum, and those below (22, 22), for the cere- 

 bellum; the upper surface of the basal process (14) is hol- 

 lowed out to receive the medulla oblongtita. 



Anterior face. 

 Fig- 89. 



Posterior face. 



