178 



GREGORY : 



NOTHARCTUS, AN AMERICAN EOCENE PRIMATE 



and the locations of their several foramina are surprisingly uniform in the Lemurinje, Indrisinse, Archseo- 

 lemurinse and Chiromyidse and that the conditions in PalcEopropithecus may be interpreted as an aberrant 

 derivative of the indrisine plan. 



Adapin^ 

 Text Figs. 59, 61 



From Stehlin's very thorough studies, first of the course of the entocarotid and its branches in an 

 injected specimen of Lemur varius (1912, pp. 1207, 1211-1213), and secondly of well-preserved crania of 

 Adapis parisiensis and Adapis ■magnus, he was able to show that Adapts, in the course of the entocarotid 

 as well as in the whole architecture of the base of the cranium, is fundamentally similar to the Lemurinse 

 and Indrisinje. The posterior carotid foramen lies at the posteroexternal corner of the bulla, below the 

 stylomastoid foramen. The canal for the art. promontorii occupies its normal position on the antero- 

 external face of the cochlea, and runs forward to the anterior end of the cavity of the bulla, medial to the 

 Eustachian foramen, entering the cranium above this point. There was no foramen lacerum medium. 

 The foramen lacerum posterius was divided into two well-separated foramina. The venous canal on the 

 laterobasal corner of the brain-cavity, through which, in Lemur, runs the cranial portion of the stapedial 

 artery, was likewise well developed in Adapis (p. 1216). This course of the entocarotid and its branches, 

 together with the entire architecture of the skull, shows that Adapis is a member of the group that includes 

 Notharctus, Lemur and Indris, and that in all probability the cerebra of Adapis, as in Lemurinse, Indrisinse, 

 etc., received their main supply from the vertebral arteries by way of the art. communicans posterior 

 or basilar artery. 



NOTHARCTIN.B 

 Plates XLIV, XLV 



The skull of N. oshorni, Amer. Mus. No. 11466, (Plates XLIV, XLV) reveals the general course of 

 the entocarotid and its branches within the bulla. The whole basicranial region is remarkably similar to 

 that of Lemur, differing chiefly in the smaller size of the bulla. The anterointernal extensions of the bullae, 

 while not extending in front of the suture between the basioccipital and the basisphenoid as they do in 

 Lemur, are joined to the posterior end of the basisphenoid so that there was no foramen lacerum medium. 

 The anterior opening of the bony Eustachian canal is situated as in Lemur. The foramen ovale was 

 external to the pterygoid plate of the alisphenoid. The cavity of the bulla was divided into external 

 and medial parts by an incomplete septum running along the cochlea, the outer chamber being the true 

 tympanic cavity, the inner being the hypotympanic sinus. The cochlea was about as large as in Lemur 

 mo7igoz and bears on its outer face the bony canal for the arteria promontorii exactly as in Lemur and 

 Propithecus, which runs forward and pierces the anterior wall of the roof of the bulla. The entrance to 

 this canal for the art. promontorii is clearly seen in the posterior carotid foramen, on the posteroexternal 

 angle of the bulla. Upon reaching the cochlea the carotid canal gives off a branch which carried the 

 arteria stapedia. The canal for the stapedial branch is of somewhat wider diameter than that of Lemur 

 varius. The stylomastoid foramen and the condylar foramen were located as in Lemur and apparently 

 also the foramen lacerum posterius was divided into two separate openings. The postglenoid foramen 

 was also identical in position with that of Lemur. 



From all this, we may conclude with practical certainty, that the whole course of the internal carotid 

 and its branches was essentially the same as in Lemur, and consequently that in Notharctus, as in Adapis, 



