NO. 4 AN ENDOCRANIAL CAST GAZIN 9 



the ridge representing the inferior petrosal sinus. This is believed 

 to represent a part of the internal carotid artery as it entered the 

 cranial cavity. It occurs nearly at the anterior extremity of the 

 petrosal and is formed by the aperture of a canal that when traced 

 within the bone seems almost certainly continuous with the canal for 

 the arteria promontorii. This branch of the internal carotid was evi- 

 dently a little larger than in Lemur and emerged relatively farther 

 forward, better separated from the hiatus Fallopii. 



Measurements of the Smilodectes endocast. — The total length of 

 the preserved portion of the endocast (U.S.N.M. No. 23276) is 

 36 mm. The combined length of the cerebral and cerebellar portions 

 from the anterior margin of the neopallium, so far as can be deter- 

 mined, to the posterior surface of the vermis as represented is about 

 32.5 mm. The length of the neopallium alone would be about 24 mm. 

 The width of the cast across the temporal lobes of the neopal- 

 lium, excluding the marginal vascular sinus, is about 29.7 mm., 

 whereas the width of the cerebellar portion excluding the lateral sinus 

 is about 20 mm. The width across the olfactory roots is estimated 

 to be 9 mm. The transverse diameter of the cast representation of 

 the medulla oblongata at the foramen magnum is about 10 mm. It 

 is estimated, from other material of this species that the length of 

 the skull to which this cast belonged was about 68 to 70 mm. from 

 the anterior margin of the premaxillae to the posterior margin of the 

 occipital condyles. 



COMPARISON OF SMILODECTES WITH NOTHARCTUS 

 AND ADAPIS ENDOCRANIAL CASTS 



Notharctus. — The most closely related form with which compari- 

 son of the endocranial casts might be made is, of course, Notharctus, 

 but known comparable material of the latter is rather inadequate. In 

 the principal specimen that Gregory (1920) cited, Notharctus "tyran- 

 nus" ( =N. tenebrosus) , American Museum No. 11478, the endocast is 

 rather poorly delineated. The top of the cast is exposed from near the 

 anterior margin for the frontal lobes to about the top of the vermis 

 posteriorly, and something of the general proportions can be ascer- 

 tained. The texture of the cast, however, is rather coarse grained so 

 that essentially no detail is evident although as Gregory noted there 

 are "vague indications of the sulcus intraparietalis." There seems, 

 moreover, suggestion of a feeble sulcus (suprasylvian?) parallel to 

 the anterolateral margin, but only on the right side. There is no 

 evidence for a pseudosylvian sulcus, but the lateral margins of the 



