570 THE BRIDGER EPOCH. 



rior to the zygomatic arch, and is in form like a trough, the inferior edge 

 being recurved from the squamosal process to the summit of the occipital 

 crest. It is narrow within the zygomatic arch, which is short, inclosing a 

 space whose length is less than one-fourth that of the cranium. 



The occipital bone extends but a short distance on each side of the 

 condyles, and is separated from the mastoid by an irregular suture, which 

 is pierced by a large mastoid foramen. On the inferior face, near to each 

 condyle, and one-third the distance from its inner extremity, is a posterior 

 condyloid foramen, isolated by a narrow bar from the extremity of the 

 foramen lacerum posterius. The paroccipital process is represented by a 

 small tuberosity, and the mastoid by a rather larger one, some distance 

 anterior to it. 



The meatus auditorius opens upward just below the external ridge of 

 the temporal fossa, and at a little distance behind the post-glenoid process. 

 Its canal contracts rapidly, and extends upward and backward toward 

 the labyrinth. It is separated from the foramen lacerum by but a thin wall, 

 and if there was an expansion of the cavum tympani it must have been 

 exceedingly small, owing to the close approximation of the mastoid to the 

 basi-occipital and sphenoid at this point. The labyrinth is lodged in a 

 petrous mass opposite the occipito-mastoid suture, and the canals are small. 



The basioccipital contracts anteriorly, and with the sphenoid forms an 

 uninterrupted boundary of the foramen lacerum This terminates opposite 

 to the posterior boundary of the external meatus, and gives rise to a wide, 

 shallow groove, which extends anteriorly between the pterygoid ala and the 

 post-glenoid process, and, turning outward round the latter, grooves it. 

 Opposite to the post-glenoid process and just posterior to the end of the 

 pterygoid, a foramen enters, which, though remarkably small, is the fora- 

 men ovale. Almost continuous with it is a canal which pierces the base of 

 the pterygoid longitudinally, and issues in an excavation of its external face 

 near the sphenoid. This is the alisphenoid canal. 



There appears to be no foramen posfglenoidale, but there is one in the 

 position of the stylomastoid on the inferior side of the mastoid bone and 

 posterior to the meatal groove. 



The pterygoids are remarkable for their great length, inclosing, as they 



