120 



BONES OF THE SKULL. 



Fig. 87 



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 occipitis), 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 



Posterior face. ^ x 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 oblongata. 



