PAL^OMASTODON. 135 



the skull and has in its posterior wall a foramen, the stylomastoid {st.mf.) ; in front of and 

 internal to this foramen the tympano-hyal [tp.h.) seems to have been situated. Between 

 this fossa and the basioccipital the bone is perforated by a large foramen for the 

 internal common carotid {i.c.c). In front the bone is produced forwards and inwards 

 into a sharp-pointed process lying along the basisphenoid and having on its inner side 

 the opening of the eustachian canal {eu.). The anterior end of this process is 

 continuous with the ridge formed by the posterior end of the pterygoid. The antero- 

 external face forms the hinder border of the foramen lacerum medium and unites with 

 the alisphenoid. 



The farietals (pa.) are unfortunately incomplete posteriorly, where, however, they 

 must have united with the supraoccipital above and with the squamosal below: 

 they helped to form the thick lambdoidal ridge, in which, as above described, 

 large air-sinuses communicating with the exterior by means of several foramina (for.) 

 were developed. The parietals are only slightly convex from above downwards and 

 incline towards one another at an angle of about 77°, meeting in a strong sagittal 

 crest (s.c), of which there is no trace in the modern Elephants. This peculiarity 

 emphasises the primitive character of this skull compared with that of Mephas, in 

 which the temporal fossae are separated by a broad expanse of skull-roof, flat or slightly 

 convex, but with no trace of sagittal crest : the difference being in the main due to the 

 fact that the development of the spongy diploe, carried to such an enormous extent in 

 Elephas, is here only beginning and does not yet extend much beyond the occipital 

 region. About opposite the anterior angle of the squamosal the sagittal crest divides 

 into the supratemporal ridges, which diverge and no doubt terminated on the post- 

 orbital processes, but unfortunately the whole of the upper part of the skull from 

 about 7 centimetres in front of the origin of the supratemporal ridges is broken away in 

 the specimen here described, and in the young example from which the account of the 

 front of the skull is taken these ridges are scarcely at all developed. Anteriorly 

 the parietals unite with the frontals, but in the present specimen only the lower 

 portion of the suture can be observed ; from this it appears that the frontals meet the 

 squamosals, so that the parietals are excluded from contact with the alisphenoid. 



The frontals, nasals, and premaxillce are wanting in the specimen upon which this 

 description is based and will be described below from another example. 



The alisphenoid (text-fig. 49, als.) may be described as a triradiate bone. Its posterior 

 portion forms the anterior boundary of the foramen lacerum medium, on either side of 

 which it unites with the tympanic : externally it joins the squamosal, the suture with 

 which runs just internal to the inner edge of the glenoid surface. This posterior portion 

 is perforated by the large foramen ovale (f.o.) and further forwards by the posterior 

 opening of the alisphenoid canal (al.c). The upper limb of the bone unites 

 posteriorly with the squamosal, and for a short distance above with the frontals. Its 

 anterior border, together with that of the lower limb, forms the prominent crest-like 



