0. a Marsh— Principal Characters of the Brontoth&ridoe. 337 



The cerebral hemispheres did not extend at all over the 

 cerebellum, and little if any over the olfactory lobes. The lat- 

 ter were of moderate size, and separated by a wide osseous 

 septum. The hemispheres were comparatively large, and much 

 convoluted. The Sylvian fissure is well-marked in the cast, 

 and some of the other principal divisions are indicated. The 

 cerebellum was small. There was a rudimentary tentorial 

 ridge. The pituitary fossa is distinctly marked. The fora- 

 mina for the optic nerves are quite small. 



The mandible in Brontotherium has a wide condyle, and a 

 slender coronoid process. The angle is rounded, and slightly 



produced downward. The symphysis is depressed, elongated, 

 ery shallow in front, and completely ossified. (Plat '"" ^ 

 The dental formula o^ Brontotherium is as follows:- 



lars, t 



Incisors,—; canines,—; premolars,— ; molars,— X 2=38. 



The upper incisors are quite small. (Plate X.) The canine is 

 short and stout, and placed close to the first premolar. The 

 upper premolars have all essentially the same structure, viz : two 

 external connate cusps, with their outer faces nearly plane, and 

 two inner cones closely united. The anterior cone is connected 

 with the opposite outer cusp by a transverse ridge, which has 

 ^°^ind it an elongated depression, more or less divided by pro- 

 ions from the outer posterior cusp. In the upper true mo- 

 , the external cusps have their outer surfaces deeply concave, 

 while the inner cones are low and separate. The lower incisors 

 were small, and evidently of little use. The two next the sym- 

 physis were separated from each other. The lower incisors are 

 not unfrequently wanting, and in old animals the alveoli may, 

 perhaps, disappear. Careful examination, however, will usually 

 show indications of them. The lower canine is of moderate size, 

 and separated from the premolars by a short diastema. The 

 lower molars are of the Palceotherium type, and agree essentially 

 with those of Menodm. 



The neck in Brontotherium was stout, and of moderate length. 

 The cervical and most of the dorsal vertebrae are distinctly opis- 

 thocoelous. The atlas is large, and much expanded transversely. 

 The axis is massive, and has its anterior articular faces much 

 broader than in the Dinocerata. The odontoid process was stout 

 and conical. The posterior articular face is concave, and oblique. 

 The transverse processes apparently bad no foramen for the 

 vertebral artery. The epiphyses of the vertebrae are loosely 

 united in most specimens, as in the Proboscidians. The lum- 

 oars are slender, and smaller than the dorsals. There are four 

 ▼ertebrae in the sacrum. The caudal vertebrae indicate a long 

 and slender tail. 



