6 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 149 



No. 17997, pi. 2, fig. 1), however, which has preserved little more 

 than the cerebellar portion of the endocast, there is suggestion of 

 a subdued fissura prima, but this may also correspond to the parieto- 

 occipital suture. The cast shows the paramedian fissure to have been 

 very well developed lateral to the vermis and the cerebellar hemi- 

 spheres are represented prominently displayed but not nearly as ele- 

 vated as the vermis. They projected very little above the general 

 level of the cerebral hemispheres and were somewhat elongate trans- 

 versely but with their long axis slightly oblique as seen from above. 

 There is no indication of a parasaggital fissure but the cast surface 

 of the lobes as well as of the vermis shows traces of the vascular 

 network of the dura mater. 



Petrosal fossa. — Immediately anteroventral to the cerebellar hemi- 

 sphere, on the surface of the cast formed by the dorsomedial surface 

 of the petrosal, is indicated the root portion of the flocculus of the 

 cerebellum which occupied a deep floccular or subarcuate fossa in the 

 petrosal. Of about the same size, directly below and medial to the 

 indicated flocculus and on the same surface of the petrosal fossa of 

 the cast is the impression of the aperture of the internal auditory 

 meatus. Immediately behind the position of the flocculus and very 

 close to the posterior bulge representing the lateral sinus can be seen 

 a small, flattened projection which corresponds to the slitlike aperture 

 of the aquaeductus vestibuli. Similarly placed with respect to the 

 pedestal representing the internal auditory meatus but somewhat 

 closer to the latter is a moderately large aperture filling which repre- 

 sents the foramen lacerum posterius. Moreover, further preparation 

 of the corresponding bone surface reveals the presence of the aquae- 

 ductus cochleae confluent with the cranial aperture of the foramen 

 lacerum posterius. Just posterior and slightly medial to the position 

 of the foramen lacerum posterius the small pyramidal form with its 

 apex directed somewhat forward is the filling of the condylar or 

 hypoglossal foramen. 



The surface of the cast formed by the anterior facing surface of 

 the petrosal, which limited posteriorly the lateral portion of the cere- 

 bral hemisphere, is very nearly at a 90° angle from the ventrolateral 

 surface formed by the petrosal. The principal structure evident on 

 this surface is the bulge at the ventral margin representing the internal 

 aperture of the foramen ovale which, incidentally, deeply notches 

 the petrosal. Also distinctive is the posterior termination, at the 

 ventrolateral margin of the surface, of the ridge representing the 

 vascular sinus that appears to follow the rhinal fissure. Directly 



