32 PROCEEDINGS OF THE IsTATIONAL MUSEUM. vol.63. 



poid leading from the generalized insectivore type of internal carotid 

 circulation to that of the Platyrrhins and all the modern Anthropoids 

 while among the modern lemurs, only those of the Madagascar group 

 may be considered as being particularly close to the Notharctid 

 stage. 



It is this condition of the internal carotid circulation in the otic 

 region, and the development of the auditory bulla in connection with 

 its relation to the tympanic ring, which Gregory especially emphasized 

 as indicating peculiarly lemurine affinities of Notharctus. Yet his 

 deductions are based almost exclusively on comparison of the Eocene 

 Notharctids with the lemurs of Madagascar, in both of which the tym- 

 panic ring is entirely free and covered by the auditory bulla and in 

 which the internal carotid artery in its course to the brain enters and 

 passes through the auditory bulla, the especial "lemurine" feature 

 being that the stapedial branch is larger than the arteria promintorii 

 portion, while in the Anthropoidea, the arteria promintorii is large 

 and the stapedial portion wanting or much diminished. 



If only the Malagasy, or Madagascar, lemurs were to be considered, 

 Gregory's presentation would be rather convincing, for there can be 

 no denying the fact that there is a striking similarity between No- 

 tharctus and this particular group of lemurs in the principal features 

 of the auditory development so far as they can be made out from the 

 bony structure. However, when the continental and other living 

 lemurs of the Old World, including Tarsius, on the one hand, and the 

 Platyrrhine monkeys of the New World on the other, are included, this 

 similarity loses much of^ts significance and, as already intimated, this 

 seems to admit of a different interpretation of relationship than the 

 one advanced by Gregory. 



As to the internal carotid arrangement observed in NotJiarctus, 

 therefore, Gregory and I seem to agree as to its being a primitive pri- 

 mate condition, but we disagree regarding its significance. 



Another important feature of Gregory's presentation is the similar- 

 ity in the relation of the annulus to the tympanic bulla observed in 

 Notharctus and the lemurs. But here again his comparison is made 

 with the Malagasy group only, and thus loses much of its significance 

 when the other living lemurs are included. In the Madagascar lemurs, 

 as is well known, the annulus is entirely free and is completely hidden 

 from beneath by the expanded bulla which extends well to the outside 

 where it is completely fused with the squamosal, without forming a 

 tubular external auditory meatus. However, in all other lemurs, in- 

 cluding Tarsius, a tubular external auditory meatus is formed appar- 

 ently from the outward extention of the annulus, which in turn is 

 fused with the bulla, a condition observed in the Old World monkeys 

 and in man. In the Platyrrhina the annulus is fused with the buUa 

 but the external bony tube is usually not developed. According to 



