298 PATAGONIAN EXPEDITIONS: PALAEONTOLOGY. 



while the dorsal portion is convex on the sides, with a broad, shallow 

 median concavity, where it extends forward between the parietals ; later- 

 ally, the occipital crest is prominent, rugose and heavy, dorsally it curves 

 forward around the median concavity already mentioned and becomes 

 very much thinner, but remains distinct and clearly demarcates the supra- 

 occipital from the parietals ; the condyles are small and sessile, project- 

 ing little behind the plane of the occiput and rather more below the 

 cranial axis. 



The basioccipital is long, broad, and concave transversely, with a shallow, 

 median depression, which deepens forward ; the paroccipital processes vary 

 much, as they may be entirely absent, or unusually prominent. A narrow 

 strip of the periotic is exposed on the surface, ending ventrally in the 

 usual, cylindrical mastoid process, with its facet for the stylo-hyal. The 

 basisphenoid is broad and nearly plane, except posteriorly, where it is con- 

 cave ; both this bone and the presphenoid are left largely exposed by the 

 pterygoids ; the orbito-sphenoid, which is quite large, is deeply impressed 

 by a fossa, into which the spheno-palatine, optic and anterior lacerated 

 foramina open. 



The parietals are large, but not very long, and support a sagittal crest, 

 which is low and thin, especially over the parietal eminence. The squa- 

 mosal is relatively small ; it forms a considerable part of the occipital crest, 

 the ventral end of which is thickened into the usual tubercle ; no distinct 

 posttympanic process is present; the zygomatic process is short and 

 slender and is bent outward so abruptly that its posterior end forms a 

 distinct angulation with the cranial wall. The lachrymals have the shape 

 common to this group, but are rather smaller and less prominent than 

 usual, an appearance which is due to the shortness of the zygomatic pro- 

 cesses of the maxillaries and to the breadth of the rostrum ; the foramen 

 proper is small, but a wide, funnel-shaped depression leads into it. 



The frontals have the ordinary hour-glass form, which is exaggerated 

 by the depth and abruptness of the postorbital constriction ; the forehead 

 is short, broad and nearly flat ; the sagittal crest, which extends over half 

 the frontals, bifurcates into low temporal ridges, which curve abruptly 

 outward and end in obscure angulations, the postorbital processes ; ven- 

 trally, the frontals are strongly incurved and take part in the fossae into 

 which the anterior cranial foramina open ; the nasal suture is a narrow 

 and deep emargination of the frontals, producing a short nasal process on 



