432 Douglass — New Species of Iferycocheerus in Montana. 



then upward again, passing just beneath the foramina at the 

 base of the inion. These foramina are not the same on opposite 

 sides of the skull. They are farther forward and farther apart 

 on the right side of the skull and are more uniform in size. 

 On the left side the anterior one is circular and several times 

 larger than the one which is a little behind and beneath it. 

 Just posterior to this smaller foramen the parieto-occipital 

 suture extends upward to the broken sagittal crest. The tem- 

 poro-occipital extends backward and downward but is lost on 

 the broken border. The ridge near the parieto-squamosal 

 suture extends from the larger foramen above mentioned, 

 downward and forward, at first coinciding with the suture and 

 then running beneath and nearly parallel to it. The brain case 

 on each side of this is broadly concave. The brain case is 

 short antero-posteriorly and slopes downward quite rapidly 

 behind the forehead, though the sagittal crest evidently con- 

 tinued nearly on a level. 



The crest of the inion is broken but was considerably pos- 

 terior to the occipital condyles. The wing-like expanses 

 extending to the zygomatic arch were broad and thin. Just 

 above the foramen magnum the occiput is broadly convex; 

 but a short distance above a depression begins on the median 

 line, becomes broader and deeper and then shallower to near 

 the crest of the inion. The ridges that bound this concavity 

 separate it from larger lateral concavities situated farther 

 down. These concavities are bounded above by the wing-like 

 expansions above mentioned and outwardly by the broad con- 

 vex post-tympanics which appear as large swellings on the sides 

 of the occiput. This post-tympanic with the horizontally 

 expanded portion of the squamosal above and the long poste- 

 rior flat surface of the post-glenoid encloses a quite large trian- 

 gular cavity, the post-tympanic and post-glenoid nearly coming 

 in contact below. The meatus auditorius externus evidently 

 did not fill all this space, but the shape cannot be definitely 

 made out on account of the matrix and injury of the bone ; but 

 it passes inward and forward a distance of 4 cm to connect with 

 the otic bullae. 



As seen from below, the foramen magnum is lenticular in sec- 

 tion and its transverse is double its antero-posterior diameter, 

 being respectively 2"5 cm and l - 2 cm . With a line joining the 

 incisive border, the lower extremities of the pterygoids and the 

 occipital condyles, this opening forms an angle of about 65°. 

 The occipital condyles are also narrow antero-posteriorly, the 

 diameter being only l-7 om in this direction while the transverse 

 diameter is 6 - l cm . The anterior articular faces are much deeper 

 and broader than the posterior ones and they are partially 





