1902.] Osborn, Dolichocephaly and Brachycephaly in Mammals. 79 



ing factors in the skull of the Titanotheres , and that they are 

 probably correlated ivith similar proportions in the trunk and 

 limbs. This result, as in the case of the Rhinoceroses, placed 

 the whole evolution of the family from its beginning in the 

 Eocene period in a new light and directly contradicted the 

 phylogenetic conclusions I had reached in 1896. 



Considering the principle, however, as only a working hy- 

 pothesis I read through various memoirs of Cope, Marsh, Earle, 

 and others on the structure of the skull in the Rhinoceroses 

 and Titanotheres and was delighted to find that dolicho- 

 cephaly and brachycephaly explained a vast number of de- 

 tailed facts which had been recorded abstractly by these 

 authors without reference to their significance, not only in 

 all parts of the skull but in the teeth. In many respects the 

 teeth were proved to conform to the skull rather than the 

 skull to the teeth. 



In brief, the proportions of the skull were found to involve, 

 as one might anticipate, every bone in the skull, but more 

 particularly nasals, horns, zygomatic arches, palate, relations 

 of the foramina in the base and side of the skull, the occiput, 

 the mastoid and other bones around the auditory meatus, 

 the premaxillary and mandibular symphyses, the jaw, the 

 diastemata between and behind the teeth, the number and 

 shape of the teeth, the shape, number, and relations of the 

 cusps, and even, it would appear, the cingulum around the 

 teeth. In other words all these characters were found cor- 

 related in many animals with the proportions of the skull, 

 and consequently with the structure of the limbs and feet, — 

 a quite unlooked for illustration of Cuvier's famous law of 

 correlation. • 



This gratifying result suggested a superficial review of the 

 mammals in general in respect to the same factors. The 

 conclusions reached in this paper are therefore of a prelim- 

 inary character. 



We may first consider the skull in itself, then the corre- 

 lation of its proportions with similar proportions in other 

 parts of the body, the exceptions to such correlation and 

 special reasons for them, some of the apparent causes of 



