develop:mekt of the skull in the ceocodilia. 277 



When the head, at this stage, is carefully peeled and stained, fine reticulations of 

 young bone-cells can be traced (PI. LXIV. figs. 8-11); these lie along the appointed 

 lines, and can be named accoi'dingly. 



The brim of the cranial basin is pyriform, the narrow end being in front (PL LXIV. 

 fig. 9) ; narrow, reticulated strips of young bone now lie along the rim and also further 

 outwards. 



The parietals are half the length of the frontals {f,l)) ; the latter are sigmoid and 

 the former crescentic. Outside the parietals we see the postorbitals and the squamo- 

 sals {j)t.o, sq), and in front of the eyeballs the small arcuate prefrontals {p.f). Over 

 the nasals sacs (na) the small nasals («) lie ; they are pyriform, with a sharp end in 

 front ; outside these are the oblong maxillaries [nix), and margining the fore face the 

 premaxillaries {px). 



The two latter pairs of bones are also well seen from below (fig. 8) ; within the 

 boundary formed by these we see a pair of fine curved styles that lie behind the middle 

 or inner nares {in) ; these are the vomers (y), their convex outline is inwards. 



So also is that of the much larger palatine bones (im), whose thick fore end is turned 

 outwards towards the maxillaries ; the transpalatines {t.pa) and the pterygoids {pg) 

 bound the hinder margin, externally and M'ithin, of the subocular palatine fenestra. 

 The transpalatines are angular and apiculate ; the pterygoids are thick in their inner 

 part, and falcate. Outside the sharp fore end of the transpalatine, lies the sharp jugal 

 style {j), and overlapping it the smaller quadrate jugal {q.j). Bony ti'aces resting on the 

 maxillary below and in front of the eyeball form the rudiment of the lacrymal, and j^'w 

 tracts of young bony tissue are appearing on each free mandible (figs. 10, 11, d, sp, cr, 

 s.ag, ag) ; the two first of these, the dentary and splenial, are the longest ; the coronoid, 

 supraangular, and angular are shorter, and invest the high hind part of the bar. 



I have not succeeded in finding any more investing bones than these, in the more 

 advanced stages, except the " basitemporals," and I have not found any endocranial 

 centre at this date ; therefore the investing bones appear first, and are almost exactly 

 sjTichronous. These bony tracts would weigh, together, scarcely more than a grain ; 

 they are sufficient, however, to form the seed-plots, as it were, of the " osteoblasts " 

 that are needed to develop the heavy bony vegetations that become the outwork of 

 the skull of the adult Crocodile. 



4th Stage. Embryos of Crocodilus palustris, 3| inches long. 



a. Chondrocranium. 



In this stage I am able to show the perfected chondrocranium before ossification sets 

 in and the visceral arches with that process just begun. 



The hind skull is now only half as long as the prochordal part ; this is mainly due 

 to the rapid elongation of the intertrabecula and the nasal capsules (PL LXV. figs. 1-4). 



