BONES ABOUT THE BRAIN
The bones containing the brain appear to be the same as form the brain case in birds. The form of the back of the skull varies in two ways. First it may be flat above and flat at the back, when the back of the head appears to be square. This condition is seen in all the long-tailed genera, such as Campylognathus from the Lias and Rhamphorhynchus, and is associated with a high position for the upper temporal bar. Secondly, the back of the head may be rounded convexly, both above and behind. That condition is seen in the short-tailed genera, such as Pterodactylus. But in the large Cretaceous types, such as Ornithocheirus and Ornithostoma, the superior longitudinal ridge which runs back in the middle line of the face becomes elevated and compressed from side to side at the back of the head as a narrow deep crest, prolonged backward over the neck vertebræ for some inches of length. All these three types are paralleled more or less in birds which have the back of the head square like the Heron, or rounded like the Woodpecker; or crested, though the crest of the Cormorant is not quite identical with Ornithocheirus, being a distinct bone at the back of the head in the bird which never blends with the skull. In so far as the crest is reptilian it suggests the remarkable crest of the Chameleon. In the structure of the back of the skull the bones are a modification of the reptilian type of Hatteria in the Lias genus Campylognathus, but the reptilian characters appear to be lost in the less perfectly preserved skulls of Cretaceous genera.
The palate is well known in the chief groups of Ornithosaurs, such as Campylognathus, Scaphognathus, and Cycnorhamphus.
Mr. E. T. Newton, F.R.S., has shown that in the English skull from the Lias of Whitby, the forms of the bones are similar to the palate in birds and unlike the conditions in reptiles. There is one feature, however, which may indicate a resemblance to Dicynodon and other fossil reptiles from South Africa. A slender bone extends from the base of the brain case, named the basi-sphenoid bone, outward and forward to the inner margin of the quadrate bone ([Fig. 22]). A bone is found thus placed in those South African Reptiles, which show many resemblances to the Monotreme and Marsupial Mammals. It is not an ordinary element of the skeleton and is unknown in living animals of any kind in that position. It has been thought possible that it may represent one of the bones which among mammals are diminutive and are included in the internal ear. The resemblance may have some interest hereafter, as helping to show that certain affinities of the Ornithosaurs may lie outside the groups of existing reptiles. Instead of being directed transversely outward, as in the palatal region of Dicynodon lacerticeps, they diverge outward and forward to the inner border of the articulation for the lower jaw which is upon the quadrate bone.
BONES OF THE PALATE
There is a pair of bones which extend forward from these inner articular borders of the quadrate bones, and converge in a long V-shape till they merge in the hard palate formed by the bones of the front of the beak, named intermaxillary and maxillary bones. The limits of the bones of the palate are not distinct, but there can be no doubt that the front of the V is the bone named vomer, that the palatine bones are at its sides, and that its hinder parts are the pterygoid bones as in birds. There is a long, wide, four-sided, open space in the middle of the palate, between the vomer and the basi-sphenoid bone, unlike anything in birds or other animals.
Professor Marsh, in a figure of the palate in the great skull of the toothless Pterodactyle named Ornithostoma (Pteranodon), from the Chalk of Kansas, found a large oval vacuity in this region of the palate. In that genus the pterygoid bones meet each other between the quadrate bones as in Dicynodon ([Fig. 73, p. 182]). Hence the great palatal vacuity here seen in the Ornithosaur is paralleled by the small vacuity in the South African reptile, which is sometimes distinct and sometimes partly separated from the anterior part of the vacuity which forms the openings of the nostrils on the palate.
The Solenhofen skulls which give any evidence of the palate are exposed in side view only, and the bones, imperfectly seen through the lateral vacuities, are displaced by crushing. They include long strips like the vomerine bones in the Lias fossil, and they diverge in the same way as they extend back to the quadrate bones. The oblique division into vomer in front and pterygoid bone behind is shown by Goldfuss in his original figure of Scaphognathus. Thus there is some reason for believing that all Ornithosaurs have the palate formed upon the same general plan, which is on the whole peculiar to the group, especially in not having the palatal openings of the nares divided in the middle line. It would appear probable that the short-tailed animals have the pterygoid bones meeting in the middle line and triangular; and that they are slender rods entirely separate from each other in the long-tailed genera.