18 MEMOIR ON THE in. 



in the last>mentioned species postero-superiorly to the orbits, the horn-cores arise. 

 The highest portion of the os frontis is between the posterior part of the bases of 

 the horn-cores, and in this position is elevated over two inches above the line of the 

 supra-orbitar margin. Anteriorly to this most elevated part, the os frontis inclines 

 at an angle of about 45, but posteriorly has a less degree of inclination. The 

 apex is transverse, obtuse, and impressed at the middle. The parieto-frontal sur- 

 face is quadrilateral, about four inches square, moderately convex, and presents a 

 broad shallow impression at its central part. 



The horn-cores curve outwards, downwards, and slightly forwards. They arise 

 about three and a half inches in a curved line from the inion, or about two and a 

 half in a straight line. They are elongated, conical, curved, and longitudinally 

 furrowed. 



The inion (Plate V., Fig. 2) is about four inches in height above the occipital 

 foramen, and in its details corresponds pretty closely with Bootherium cavifrons. 



The relative position of the orbits to the horn-cores is the same as in the species 

 just mentioned. The supra-orbitar margin is about two inches below the highest 

 part of the base of the horn-cores, and these commence anteriorly about the poste- 

 rior sixth of the entrance of the orbits. At its anterior third, the supra-orbital 

 margin is deeply notched, and the supra-orbital process upon the upper or frontal 

 surface, about an inch and a half from the margin, is pierced by three foramina 

 arranged in an antero-posterior row. 



In advance of the orbit, the lachrymal bone is depressed into a remarkably deep 

 fossa, or larmier, which appears to have been hemispherical, but, in the specimen, 

 the lower portion is broken away (Plate IV., Fig. 2). At the orbital margin, below 

 the larmier, a deep, broad, lachrymal groove exists, as in Bootherium cavifrons. 



The temporal fossa presents nearly the same degree of inclination as in the 

 latter, and also has the same relative degree of shallowness and length and 

 breadth of surface which this has in "comparison with that of the Buffalo. 



The ridge, which in Bootherium cavifrons proceeds from the frontal process late- 

 rally, beneath the base of the horn-core, is but very feebly developed in Bootherium 

 bombifrons. 



The base of the cranium, though much mutilated, is sufficiently well preserved 

 to exhibit the peculiarities which associate it in the same genus with Bootherium 

 cavifrons. The foramina and processes have the same relation of position and 

 form. Like in the latter, the occipital condyles appear to have been less bent than 

 in the Buffalo, the paramastoids have been large and robust, and the fossae between 

 them and the condyles have been superficial also, as in Bootherium cavifrons. 



The basilar process is broad and strongly marked by processes for muscular 

 attachment. 



The form of the os petrosa, auditory process, and relative position of the meatus 

 auditorius are the same as in Bootherium cavifrons. 



The post-glenoid tubercle is relatively larger than in the latter, and between it 

 and the auditory process is a pit, into which opens a large foramen, piercing the 

 root of the zygoma, from the temporal surface. Both the pit and foramen exist, 

 but are much smaller, in Boottierium cavifrons. 



