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 {tpJi.) seems to have been situated. Between 
this fossa and the basiocci[)ital 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 {eii.). 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 parietals {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 Elephas, 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 tbe 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. 
T\\e frontals, nasals, premaxillm 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 
