182 



GREGORY: NOTUARCTUS, AN AMERICAN EOCENE PRIMATE 



in the orbit, wliich appear to have been supphed originally by the first visceral arch, are found in certain 

 adult mammals to be supplied by the main vessel of the second visceral arch, which is the stapedial 



artery. Again the minor branches of the stapedial artery 

 are often captured by the main trunk of the third visceral 

 arch, which is the external carotid, and as a result of this 

 capture the stapedial artery itself is often absent in the 

 adult although present in the embryo. 



According to this theory the insectivores, as de- 

 scribed above, have a more primitive type of entocarotid 

 circulation than that of the lemurs, and the lemurs in 

 turn are more primitive than the tarsioids and higher 

 primates. In Erinaceus, as we have seen, the stapedial 

 artery is fully developed and retains both its main branches, 

 the ramus superior and ramus inferior with all their minor 

 l)ranches. In lemurs the arteria promontorii or true 

 carotis interna is progressively reduced, the external 

 carotid has "captured" the arteria maxillaris interna or 

 orbital continuation of the ramus inferior, and the tym- 

 panic portion of the ramus inferior has been lost. The 

 same condition is indicated in Notharctus and Propithecus 

 by the total lack of a foramen caroticum alisphenoidei 

 posterior in the anterior wall of the tympanic fossa. In 

 the Lorisidse and Tarsiidae the whole stapedial artery is re- 

 duced or wanting but in these families the true internal 

 carotid is enlarged, and, according to Tandler, in the 

 Lorisida? enters the cranium through the foramen lacerum 

 medium, in front of the bulla, while in Tarsius it pierces 

 the middle of the bulla. In man and other Platyrrhini 

 (including both New World and Old World genera) ac- 

 cording to Tandler, the arteria promontorii or true inter- 

 nal carotid is large, traversing the periotic through the 

 carotid canal; the stapedial artery and the tympanic 

 portion of the ramus inferior are usually reduced or want- 

 ing, while the distal branches of the ramus inferior are ap- 

 propriated by the carotis externa. 



From this review it appears that, if Tandler's 

 observations and hypothesis are correct, the entocarotid 

 distribution in Notharctus and other lemurs is structurally 

 ancestral to those of higher primates, except that in 

 Lemuridse the arteria promontorii is reduced, while the 

 TarsiidjB resemble the Platyrrhini in the enlargement of 

 the arteria promontorii and in the reduction of the arteria 

 stapedia. 



pattorn of 



showing the co\ii 

 trteries in (1) Ki 

 AftiT Tandler. 

 ■iiniiHnis. The jiriiiiiti' 

 the carotid syslcm is nearly- intact, save for the loss of a 

 branch connecting ihc cainiis cxlcrna (c.e.) with the ramus 

 inferior {r.i.). The arteria sta])edia {A.d.) retains both 

 rami, superior (r.s.) and inferior (r.i.). 



(2) Lemur varius. The external carotid (c. c.) has 

 captured the vessels formerly supplied by the ramus in- 

 ferior, which in the existing lemurs has disappeared. The 

 true internal carotid (art. promontorii, c. i.) is reduced. 



(3) Man. The external carotid has captured the 

 whole system that was formerly supplied by the stapedial 

 artery; the latter is lacking except in embryonic stages. 

 The internal carotid (art. promontorii) becomes very large. 



