OF THE RED CRAG. 



13 



condition of that upper mid-tract of the rostrum which Cuvier made distinctive, with 

 other specific characters, of his ZipJiius pJanirodris and Zijjhius longirostris. 



I find this character in the composition of the rostrum of the skull of an adult male of 

 Ziphius Layardi {Bolkliodon, Gray) liberally transmitted, like that of Z. ifidicus, for 

 description, to the British Museum, by the excellent naturalist, Mr. Edgar L. Layard, 

 P.L.S., &c., now at the Cape of Good Hope, after whom the species is named.^ 



In this skull (PI. I) the premaxillaries (fig. 1,22') retain, at their hind part, the sutures 

 connecting them with the nasals (15) and maxillaries (21'), where they bound the upper 

 apertures of the nostrils ; the sutures connecting them with the prefrontal (figs. 1 and 2, 

 14) and maxillaries are tniceable a short way along the base of the rostrum, and then 

 become obliterated, that with the prefrontal being the first to disappear. Upon the fore 

 part of the palate (ib., fig. 3) the sutures remain between the premaxillaries (22) and the 

 vomer (13), and between the premaxillaries and the contiguous palatine parts of the 

 maxillaries (21). 



I may here recall the remark made in discussing the homology of the ' prefrontals,'^ 

 viz., that the toothed Cetacea afford welcome and favorable grounds for determining the 

 nature of the mammalian ethmoid through the absence of the olfactory sense-capsules which 

 obscure the homologies of the prefrontals in the rest of their class. The ' os en ceinture, 

 Cuv., of Batrachians, and the similarly conspicuous rhomboid tract of the ' ethmo'ide,' Cuv., 

 on the upper and middle part of the base of the rostrum in Struthious Birds, exhibit the 

 partially exposed condition of the prefrontals characterising certain species of Ziphius. In 

 this, as in other Cetacea, the prefrontals, prior to their coalescence as ' lamina perpendicu- 

 laris,' diverge and contribute a small share to the anterior wall of the cranium and a larger 

 one to the posterior walls of the nasal passages, of which their produced and coalesced 

 parts constitute the partition ; they are connate posteriorly with the orbito-sphenoids, and 

 usually coalesce with the vomer inferiorly. I have observed the coalesced ' lamina per- 

 pendicularis' to be cartilaginous in a young whale's skull where the rest of the walls of 

 the nasal passages w^ere ossified. The forward continuation of the ' lamina perpendicularis 

 aethmoidei' rests upon the groove of the vomer, in a cartilaginous state, in most Cetacea, 

 leaving the vacancy in the dry skull along the upper medial line which suggested to 

 Cuvier the term ' cavirostris' for the Ziphius which he first made known to zoologists.^ 

 In the present species {Z. Layardi) it is ossified, and, becoming superficial and conspicuous 

 between the premaxillary nasal processes, expands as it advances, and rises as a smooth, 



1 The want of definitions of bones or sutures in the descriptions and figures by Dr. J. E. Gray, F.R.S., 

 of this instructive specimen, in the ' Proceedings of the Zoological Society,' April 11, 1865, p. 358, and in 

 his very useful ' Catalogue of Seals and Whales in the British Museum,' 8vo, 1866, p. 354, has not enabled 

 me to use or reproduce them for my present purpose. 



2 "On the Homologies of the Vertebrate Skeleton," 'Report of the British Association," 1846, 

 p. 226. 



^ The section of the skull of Euphysetes simus in my paper " On Indian Cetacea," ' Zool. Trans.,' vol. vi, 

 pi. xiv, figs. 1, 10,14,13, '^'^^ student of homologies in following the above remarks. 



