No. 5.] 



SHUFELDT ON THE OSTEOLOGY OF EREMOPHILA. 



121 



the same as in the last example (it being, however, the inner facet of 

 two on the tympanies, as a rule), the combined angles, or either of them 

 separately, is very small, or the base and foramen may be found to lie 

 nearly in a plane parallel to the plane upon which the skull rests, or the 



angles are 0°. We see then that in the present case, the bearing points 

 being given, the angle of the combined planes is 40°, which fact, even 

 ■without actually taking the angles in question, conveys to our minds 

 about the "pitch" or relation of the basi-cranii to the other salient fea- 

 tures of the skull. Taken accurately, these angles, it is obvious, would 

 have a certain vakie when we come to comi^are the various skulls of the 

 class. 



The primary elements of the occipital, or first cranial vertebra, have 

 become completely fused together, and with such other bony elements of 

 the vertebra beyond, of the mesencephalic arcli, with which they usually 

 articulate. The well-marked superior curved line that limits muscular 

 attachment above would seem to be, and in all probability is, about the 

 position of the lambdoid suture, and the suijerior boundary of the bone 

 we are describing. This curved line descends and is gradually lost along 

 the boundaries of the mastoids and occipitals on either side. Exter- 

 nally and inferiorly we find the occipital pierced by the usual foranuna 

 of the basi-cranii. The group for the exit of the eighth pair of nerves, 

 being the most anterior of all, are situated on either side, in well-marked 

 depressions or pits, some 7 millimetres apart. Back of these and nearer 

 together are the minute precondyloids, looking forwards ami outwards for 

 the i^assage of the hypoglossal nerves. These last foramina are just an- 

 terior to the border of foramen magnum ; this latter aperture is of good 

 size, comparative!}', having antero-posterior and transverse diameters 

 of 3 millimetres each, with an additional millimetre for the oblique 

 diameters, making the latter 4 millimetres each. It is subcircular in 

 outline, its anterior rim passing around a depression that lies just in 

 front of the condyle, giving the latter the appearance of jutting out 

 into the foramina! space. The condyle is nearly sessile, having the 

 merest trace of a neck, hemispheroidal in form, with ;in luM-izontal 



