94 FOSSIL REPTILIA OF THE 



laterally with the paroccipitals (PI. XXVI, fig. 1,4); but between these and the basisphe- 

 noid it joins the mesially inclined hinder end of the pterygoids (ib., 24). The apex of 

 the superoccipital (3) is wedged into the interspace of the hinder bifurcation of the parietal 

 bones (/'), which it underlaps and partly supports ; its base forms the upper border of the 

 foramen magnum. The paroccipitals (ib., 4, 4), broadest where they join the basioccipital, 

 contract as they extend outward into a strong triedral bar, which abuts against the 

 tympanic (28), at the interval between the mastoid ( 8 ) and pterygoid (24). 



The centrum (l), neurapophyses (2), neural spine (3), and parapophyses (4) of the 

 hindmost cranial vertebra are instructively demonstrated by the Ichthyosaurian condition 

 of the ' occipital bone ' of Anthropotomy. 



The basisphenoid (PI. XXV, fig. 1, 5) presents, on its under and outer surface, the 

 form of an irregular, subquadrate plate, narrowest behind, where it joins the basioccipital, 

 expanding as it advances, the anterior border presenting a rough, sutural, notched 

 surface, at its middle third, for the presphenoid (9), and a smooth emargiuation on each 

 side forming the hind border of the sphenopterygoid or ' interpterygoid ' vacuities ( s , s). 1 

 The hinder half of the under surface of the basisphenoid presents shallow rough depres- 

 sions and feeble risings for muscular attachments, and, like the basioccipital, it is 

 imperforate. Of the alisphenoids I have been unable to determine more than their 

 presence and their small size. The side walls of the brain-case proper seem to have been 

 mainly cartilaginous. 



The parietals (7) in most Ichthyosaurian skulls retain their median (sagittal) suture 

 (PI. XXIII, fig. 1, 7), which usually opens out anteriorly to form the hind end of the 

 ' foramen parietale ' or fronto-parietal fontanelle 2 (/), the chief part, or whole, of which is 

 bounded by the frontals (11). 



The upper surface of the parietals seems, by reason of the aspect of the occipital por- 

 tion, to be divided by a ridge (r) extending from the mastoids (8''), and continued upon 

 the parietals to their mid-suture, into an anterior (7) and posterior (7') surface. This masto- 

 parietal ridge (s" r) properly bounds, above, the occipital surface, to which the parietals 

 thus contribute about a fifth part of their length above the superoccipital bone (PI. XXVI, 

 fig. 1, 7'). Anterior to this ridge each parietal slopes to the temporal fossa (PL XXIII, 

 fig. 1, t), the parietal surface being divided by a low longitudinal rising continued forward 

 from a posterior convexity into two facets, both of which are concave across. The dividing 

 ridge is overlapped by a postero- mesial angle of the postfrontal (12), between which and the 

 frontal a narrow forward continuation (7") of the parietal is exposed, which overlaps the 



1 ' Anatomy of Vertebrates,' vol. i, p. 157, fig. 98, D, 5. 



2 "This foramen, or 'fontanelle,' is common in the Triassic Reptilia. It is described and figured in 

 Galesaurus, Petrophryne, Dicynodon, Ptychognathus, Oudenodon, Kisticephalus, and Procolophon ; in the 

 latter it is targe. It is wholly ' parietal ' in Kisticephalus and Ptychognathus, in which it is placed far 

 back." — 'Descriptive and Illustrated Catalogue of the Fossil Reptilia of South Africa in the British 

 Museum,' 4to, 1876. 



