BY W. J. McKAY. 905 



made up of the first and second parts of the nerve emerges in 

 front of the alisphenoid, the posterior division behind. The small 

 foramen for the seventh nerve is slightJy posterior to the foramen 

 ovale, while the eighth nerve emerges from a foramen placed close to 

 the junction of the prootic with the epiotic. The bone also forms 

 portion of the anterior boundary of the fenestra ovalis. It has the 

 greater portion of the anterior semicircular canal running upwards 

 and backwards to the epiotic, and it also has the anterior portion 

 of the horizontal canal running forward to join the anterior. 



The epiotic is closely united to the supraoccipital bone, and 

 more anteriorly with the superior plate of the parietal. Inferiorly 

 it joins the prootic, posteriorly the opisthotic. It contains the 

 superior parts of the anterior and posterior semicircular canals. 

 Portion of the digastric muscle arises from its external surface. 



The opisthotic is in contact with the epiotic above, the prootic 

 in front, the basioccipital below, and the exoccipital behind. It 

 contains the chief part of the posterior semicircular canal which 

 runs upwards and forward to end in the epiotic above. It also 

 has the posterior portion of the horizontal canal running from the 

 prootic in front. " The opisthotic forms the back margin of the 

 fenestra ovalis, and forks in the fenestra rotunda nearly enclosing 

 it" (Parker). 



Os ALISPHENOIDErM. 



Alisphenoid, Parker, Parker and Bettany, Hoffmann. 



The alisphenoid is a small quadrilateral-shaped line. It lies 

 across the foramen ovale, and thus divides this orifice into two 

 moieties. Its anterior border is concave, and forms the posterior 

 rim of the anterior of the two orifices of the foramen ovale which 

 transmits the first and second divisions of the fifth nerve ; the 

 posterior border bounds the foramen which transmits the third 

 division. The superior border is joined to the prootic, while the 

 external surface is smooth, and is in contact with the parieto- 

 [tterygoid muscle. A small foramen is present in the lower 

 portion of this external surface ; this transmits the nerve that 



