ART. 1. PRIMATES OF THE FORT UNION GIDLEY. 31 



tory region, both of which are found in Notharctus in practically the 

 same stage of development as in the Madagascar lemures. The first 

 of these seems to have little or no weight as a proof of afiinity be- 

 tween an ancient Eocene group and living forms, when it is considered 

 that all Primates which finally attain the condition of having the 

 orbit separated from the temporal fossa by a bony partition, as in 

 the living Anthropoidae, must have passed through just this stage at 

 some time during its development. If, therefore, this feature has 

 any significance, it is to the effect that it seems too advanced a stage 

 for any true lemur at so early a geological age, and is about what 

 would be expected in an Eocene anthropoid. 



As to the modifications of the auditory region, here again the simi- 

 larities of Notharctus to the Madagascar lemurs, pointed out by Greg- 

 ory, seem to represent similar stages reached in development, rather 

 than especial relationship. These similarities, consist principally in 

 the presence of a bulla which covers over the petrous portion of the 

 mastoid below and inclosing the tympanic ring; the course and dis- 

 position of the internal carotid artery and its principal (stapedial) 

 branch; and the form of the cochlea. First of all, these characters 

 would not apply, as already conceded by Gregory, when comparisons 

 are made with the non-Malagasy lemurs. Therefore it would seem 

 that the most which can be claimed for the possession in common of 

 these characters by Notharctus and the Madagascar lemurs is that 

 they are primitive primate characters to be expected in the former, 

 because of the early geologic period, and which have been retained in 

 the latter along with other primitive features. Therefore they can 

 mean little or nothing as determining phyletic relationship. 



The presence in Notharctus of a bony canal through which the inter- 

 nal carotid artery passes over the ventral surface of the petrosal to 

 enter the brain case, and its relative size compared with the stapedial 

 branch, is, however, an important feature in considering the possible 

 affinity of the Notharctid group with any branch of the Anthropoidea. 

 It would seem to be the primitive condition in the Primates that this 

 artery was relatively small and of less importance in supplying the 

 cerebral hemispheres with blood, and became more important for this 

 function in proportion as the brain increased in size. Thus the rela- 

 tive size of the internal carotid canal is observed to increase and the 

 stapedial branch to decrease, as noted by Wortman^^, from the small- 

 brained to the large-brained forms. 



It is, therefore, at least significant, that in the relatively small- 

 brained Notharctus of the Eocene, which has the stapedial branch 

 relatively large, the two main branches of the internal carotid are in 

 just the position and condition to be expected in a primitive anthro- 



'•Aracr. Joum. Sci., vol. 15, 1903, p. 153. 



