Misceiianeotts, 389 



like ordinary transverse processes, broadest where they join the basi- 

 occipital, and extending outwards to abut by a truncated end against 

 the tympanic pedicle. The centrum, neurapophyses, neural spine, 

 and parapophyses of the last cranial vertebra are unmistakeably 

 demonstrated by the Ichthyosaurian condition of the 'occipital bone' 

 of Anthropotomy. The basisphenoid is an irregular subquadrate 

 plate, narrowest behind, where it joins the basioccipital, expanding 

 as it advances forwards; the anterior margin presenting a rough 

 sutural surface at its middle third for the presphenoid, and a smooth 

 emargination on each side of this forming the hind boundary of the 

 spheno-pterygoid vacuities. The hinder half of the under surface of 

 the basisphenoid presents slight rough tuberosities and depressions 

 for muscular attachment, but no processes; and, Hke the basi- 

 occipital, it is imperforate. The upper or cranial surface has a me- 

 dian pit. Of the alisphenoids I can at present state nothing more 

 precisely than their very sm.all size. The major part of the proper 

 side-walls of the cranial cavity seems to have been cartilaginous in 

 the Ichthyosaurus, 



The parietals in some Ichthyosauri retain their median suture, 

 from which each bone slopes downwards and outwards, forming, at 

 the anterior three-fourths, a surface at first concave, then convex : 

 the concave part belongs to the upper region of the skull ; the convex 

 part passes down to form the inner wall of the temporal fossa : the 

 above part of the parietal is divided by an oblique ridge from the 

 posterior fourth of the bone, which is roughened for the insertion of 

 a strong nuchal muscle, and might be regarded as part of the occi- 

 pital as well as of the upper region of the cranium. The above ridge 

 is continued on to the upper part of the mastoid, and seems to form 

 the true upper boundary of the occipital region, the posterior borders 

 of the parietal forming a lower second ridge in that region. Of the 

 part of the parietal in advance of the upper ridge, the upper and 

 fore part is concave, the hinder part convex : the concavity is divided 

 by an obtuse angle — scarcely a ridge — from the part which sinks 

 more vertically into the temporal fossa : this angle is continuous with 

 the anterior border of that fossa, so that the crotaphyte muscles may 

 not have had their origin extended upon the upper concave surface. 

 The hinder and outer angle of the parietal is overlapped by the mas- 

 toid, and extends to within a third of its lower end, forming part of 

 the sides of the occipital surface, and bounding there, externally, the 

 vacuity between the exoccipital, paroccipital, lower part of mastoid, 

 and the above part of the parietal. The median sutural borders of 

 the parietal diverge anteriorly to form the hind half or third of the 

 * foramen parietale :' the fore part of each parietal extends further 

 forwards, outside the extremities of the frontals which form the front 

 part of the ' foramen parietale ;' and it articulates with the frontal 

 and })ost-frontal. 



The mastoid is a strong triradiate bone, the rays inclining forwards 

 from the centre, which forms the obtuse prominence at each postero- 

 lateral angle of the skull. The upper ray is three-sided, the two 

 upper sides smooth and sloping from the ridge, which is continued 



