On the interior of the brain case is the cavity for the brain which indicates that this organ was of diminutive size, measuring about 150 mm. in length by 50 mm. in width at the widest part. It indicates a brain with very small cerebral hemispheres, which, however, had a swollen posterior margin, a larger cerebellum, and a wide medulla oblongata. The impression which I obtained of this brain is strikingly like that given for _Palaeomastodon_. On either side of the brain cavity are a couple of vacuities, apparently for lightening the weight of the skull. At the inner end of the auditory meatus is a large ear chamber, divided into a smaller anterior or cochlear portion, and into a larger posterior ear chamber proper. [Illustration: Fig. 109. Palatal views of the basicranial region of A. Pyrotherium, and B. Palaeomastodon, for comparisons; _alc._, alisphenoidal canal; _als._, alisphenoid bone; _Bsp._, basisphenoid bone; _eu._, Eustachian canal; _f.l.m._, foramen lacerum medium; _f.l.p._, foramen lacerum posterior; _f.o._, foramen ovale; _i.c.c._, foramen for the internal common carotid; _mx._, maxilla; _oc.f._, occipital foramen; _pal._, palatine bone; _p.p.f._, post-palatal foramen; _pt._, pterygoid bone; _pt.s._, and _p.ty.sq._, post-tympanic process of squamosum; _sq._, squamosum; _st.m.f._, stylomastoid foramen.] In figure 109, I have placed a diagram of the base of the skull of _Pyrotherium_, along beside that of _Palaeomastodon_, for comparison of the basicranial foramena. The skull of _Palaeomastodon_ is somewhat more elongated, especially in the posterior part. In both, there are two antorbital foramena; the post-palatal foramena of _Pyrotherium_ are a trifle further back, but this palatal region in both is of the same type which is peculiar to elephants and _Pyrotherium_. In _Pyrotherium_ the condylar foramen is separate, while in elephants it is fused in with the foramen lacerum posterior. This latter foramen in both cases is situated just back of the tympanic, and in _Pyrotherium_ is of considerably larger size than in _Palaeomastodon_. The foramen lacerum medium is in front of the tympanic and in _Pyrotherium_ appears considerably larger, mostly because it is under the margin of the tympanic in _Palaeomastodon_. The foramen for the internal common carotid in _Palaeomastodon_ pierces the tympanic bone just to the inside of the middle line, while in _Pyrotherium_ it is on the outer margin of the tympanic. The Eustachian canal is on the external border of the tympanic in both cases, but in _Pyrotherium_ it is further back. The foramen ovale of _Palaeomastodon_ is in the posterior part of the alisphenoid bone, but with the shorter alisphenoid of _Pyrotherium_, this foramen is pushed back to the posterior margin of the bone. In both cases, the alisphenoidal canal starts under the base of the fused alisphenoid and pterygoid, and opens into the orbit. The stylomastoid foramen of _Pyrotherium_ is situated further out than in the case