AESINOITHEEITJM. 15 



partly filled in life by the tympanic, which is wanting in all the skulls hitherto 

 examined. The upper posterior edge of the pterygoid within this opening forms 

 the inner border of a deep groove lying between it and the squamosal and probably 

 representing the foramen lacerum medium (the foramen lacerum anterius of some 

 German authors). 



As already remarked, the boundaries of the alisj)henoid and orlitosphenoid are 

 by no means clear. The alisphenoid appears to send down a long narrow plate to 

 the outer face of the vertical palatine plates, with which its lower end is intimately 

 fused, forming a prominence which is seen in PI. I. at the end of the reference-line 

 running from the letters ^Z. Further up, this alisphenoid plate is perforated by the 

 short wide alisphenoid canal (text-fig. 4, al.c), the anterior opening of which lies within 

 the anterior edge of the plate, which is continued upwards and forwards as a prominent 

 downwardly directed crest of bone, forming the outer side of a deep groove, at the 

 bottom of which there are several foramina in addition to the alisphenoid canal. The 

 most important of these is a large somewhat vertically elongated opening, the foramen 

 lacerum anterius {foramen sphenoidale of some authors). Above and slightly internal 

 to the foramen lacerum anterius, and separated from it by a narrow bar of bone, is the 

 smaller and more rounded optic foramen (Pis. I., II. ; also text-fig. 4, ii.) opening 

 into a groove, of which the upper edge is constituted by a continuation of the 

 crest formed by the border of the alisphenoid plate, the lower edge being much 

 less prominent and probably approximately marking the lower border of the 

 orbitosphenoid, in which the foramen itself is no doubt situated. Above and 

 in front of the optic foramen there is a very small aperture, probably for a 

 blood-vessel. 



Several more or less nearly complete casts of the cranial cavity have been made, 

 that upon which the accompanying figures (text-fig. 5) are based being taken 

 from the skull figured on Pis. I. and II. (M. 8463). It is the only one in 

 which the prominence marked and. is shown, in consequence of the partial 

 preservation of the inner portion of the periotic. In all the others the loss of 

 the auditory bones leaves a large vacuity on either side of the basicranial axis, 

 as above mentioned. 



A detailed account of the brain-cavity will not be attempted, and some of the 

 more important characters only are here referred to. The olfactory lobes (ol.) 

 are large, but not so large in proportion to the rest of the brain as in the 

 Amblypoda. The cerebral hemispheres (h.) are far more developed than in that sub- 

 order, the frontal region being especially prominent and rounded. The surface of the 

 cast is almost smooth, and in the absence of a distinct rhinal fissure it is difficult to 

 say what portion of the cerebrum belonged to the neopallium. The only trace of 

 a sulcus seems to be that marked s., running upwards and backwards on the side 

 of the brain from behind and beneath the olfactory lobes. 



