298 PROF. W. K. PARKBU ON THE STEUCTUEE AND 



these passages the united bones form a small styloid partition. Nearly half the median 

 part of the pterygoids is united by suture to form a continuation of the " hard palate," 

 which in front is formed by the premaxillaries and the maxillaries ( px, mx), and in the 

 middle by the long, narrow, subtubular palatines [pa). The pterygoids can still be 

 peeled off the basisphenoid in ripe (or nearly ripe) young (PI. LXX. figs. 4, 5, pg, b.s). 

 When the lower bony floor has been removed (PI. LXX. fig. 3), the relation of the 

 vomers [v), palatines ( pa), and pterygoids [pg) to the basis cranii is shown. At first the 

 vomers appear to be merely styloid bones, with their pointed end behind; but the 

 pointed part has a thin curved flange, which is coadapted to tlie upper plate of the 

 palatine of the same side. The pterygoids run forward between the vomers, and end 

 there as sharp styles ; they are scoops, with their hollow part downwards ; further back, 

 they unite into one, with a median crest looking downwards. All this is in the fore 

 half; behind, these bones grow into deep wide wings, but up to the posterior nares 

 they are tubular. 



The lacrymal bone (PI. LXX. fig. 2, I) has completed its tube. The bones of the 

 hind face have finished the temporal and zygomatic arches, also the splints of the 

 mandible (PI. LXIX. figs. 9, 10) are fairly complete. 



The sectional views (PI. LXX. figs. 12, 13) show the thickness of the splint-bones, 

 and their relation to the endocranial elements. 



8th Stage. Adult Crocodiles and Alligators. 



For descriptions of the skull of the adult I must refer the reader to the works men- 

 tioned in the " Bibliographical list" (p. 264), and especially to Professor Miall's valuable 

 " Study." That work, witli the actual skull of a full-grown Crocodilian, will enable the 

 worker to finish this "demonstration." 



General BemarJcs. 



A more difficult task will be the comparison of the skull of this type in its various 

 stages with tlie skulls of other Sauropsida in their various stages, and then to see 

 how these oviparous, amniotic types, each in their own way, specialize their skulls and 

 from the most similar elements develop such dissimilar skulls as those of a Snake, a 

 Tortoise, a Lizard, a Crocodile, and a Bird. 



I am able now to refer the reader to memoirs on all these (including the present 

 paper) ; they are to be found in the ' Transactions ' of the Microscopical, Linnean, 

 and Royal Societies, of this Society and in the first volume of the ' Eeports of the 

 Challenger ' (that on the skull of the Sea-Turtle). 



It seems therefore that, to give completeness to the present paper, I ought to point out 

 the more important modifications seen in the skull of the Sauropsida — how that skull 

 is a mere specialization of the underlying Ichthyic type, and in what manner and degree 



