Page:Quarterly Journal of the Geological Society of London, vol. 27.djvu/327

1871.] processes. These in their present abraded state are obtuse four-sided pyramids, the lower side of which looks downwards, and contributed to form the orbit ; another side looks backwards, and belongs to the temporal fossa ; a third is directed upwards, and forms part of the sinciput ; and the fourth, directed forwards, is part of the fractured surface left by the separation of the facial segment of the skull. Behind, the temporal fossae are limited by the outer and anterior surface of strong, trihedral, divergent, suspensorial processes (sp) directed outwards and backwards, from which the quadrate bones depended. The roof of the skull in front is broad and transversely convex, and above the middle of the temporal fossae it contracts so much that here it might be properly described as crested (pa), the sides sloping almost vertically from the mid ridge, with only a slight outward inclination, as low as a horizontal groove running from front to back along the temporal fossa, and marking, perhaps, the meeting of the lower border of the parietal bone with those forming the side-walls of the skull. Behind, the narrow crested part of the roof forks and sends outwards and backwards the usual divergent parietal processes of lacertilian skulls. An obscure serrated transverse line about .5 inch behind where the facial segment has broken away is, perhaps, the suture between the parietal and principal frontal bone. No parietal foramen is discernible. That part of the parietal bone which roofs the front of the cranial cavity is very dense ; it attains a thickness of .9 inch. The hinder part of the roof is even thicker, but it is much less solid and consists principally of cancellous tissue.

Viewed from behind (fig. 4), the outline of the skull is an inverted triangle. The left suspensorial process, forming the upper and outer angle, on this side is wanting ; and the end of the right one (sp) is abraded. On the right side the whole of the surface above the foramen magnum is much splintered ; but the splinters having become reunited with very little displacement, its form is not much changed. When the floor of the cranial cavity is horizontal, the part of the occipital surface immediately above the level of the foramen magnum looks downwards and backwards, while the greater part of the surface above this looks upwards and backwards, and it makes now an obtuse angle with the sinciput ; but as the meeting line of the occiput and sinciput is somewhat crushed in and worn, the angle may originally have been much smaller. This incrushing has been favoured by the presence here of the cancellous tissue already mentioned. The foramen magnum (f) is subcordate (in the language of botanists). Its vertical diameter is 1.4 inch, and its transverse one 1.6 inch. Directly above the foramen is a slight mesial swelling, from which a low horizontal ridge is produced outwards. Laterally, below this ridge the surface is gently hollow. The occipital condyle (ot) roughly resembles a horseshoe. Its upper surface is deeply grooved. Its transverse slightly exceeds its vertical diameter. It projects considerably behind the general plane of the occiput ; and below, at the under surface of the skull, a deep constriction separates it from the parts immediately in front, making it nearly pedunculated.

The base of the skull (fig. 5) offers an extremely irregular surface.