THE SKULL. 19 



c. External to these is the I^ly^qy foramen lacerum 

 posterius^ which gives exit to the pneumogas- 

 tric and spinal accessory nerves (i8o, h). 



d. Still farther out is seen the conical post-auditojy 

 process, covered over by the squamosal bone. 



e. Above the foramen magnum the bony spine of 

 the supra-occipital bone projects backward ; on 

 each side of this the roof of the skull is con- 

 cave, and in the bottom of the hollow is a 

 large foramen, through which the external caro- 

 tid artery passes out to supply the exterior of 

 the head. 



26. On the Base of the Skull, note : 



a. The ventrally projecting quadrate bone, with its 

 terminal facet for articulation with the mandi- 

 ble. 



h. Farther forward, and near the middle line 

 the posterior nares^ and somewhat behind and 

 to the outside of these, the aperture on each 

 side for the transmission of a branch of the 

 fifth cranial nerve. 



c. In front of the quadrate a large aperture leads 

 up into the orbito-temporal fossa ; through it 

 the main muscles of mastication formerly 

 passed to the lower jaw from their origins on 

 the sides of the brain-case. 



d. Behind the quadrate is a plate of cartilage, 

 ossified in some specimens, which is often re- 

 moved in cleaning the skull; if this has not 

 happened remove it now on one side. This 

 will lay open part of the labyrinth and the inner 

 section of the tympanic cavity, which will be 



