10 



BRITISH rOSSIL CETACEA 



The prcmaxillarics then expand and diverge (22'), curving outward and upward to articu- 

 kite with the sides of the basal half of the short and massive nasals (15). These are 

 rather turned to the left. The nasal plate of the right premaxillary (22') is broader and 

 less vertical than that of the left ; it is, as it were, pushed somewhat outward and down- 

 ward. The kind and degree of this symmetry closely resemble those described and figured 

 by Cuvier in his type- specimen of Ziphius caviroslris} 



The cavit}^ so circumscribed or bounded externally by the premaxillary plates, answers 

 to that marked d in figs. 4, 5 and 6, of pi. xxvii, op. cit., of Cuvier's Ziphius planirostris ; 

 we shall find it common to all the ZipJdi, with varying proportions [such as are exhibited 

 by the recent Ziphius Layardi, PI. I, fig. 2, of the present Monograph]. The maxillaries, 

 forming, in Ziphius indicus, the lower and lateral parts of the rostrum to within about 

 three inches of its free end (fig. 5, 21), gradually expand vertically and transversely as 

 they pass backward, bending inward below, along the palato-premaxillary and palato- 

 vomerine sutures, until the right meets the left maxillary at the niid-hne (fig. 7, 21), in 

 advance of the palatine bones (ib., 20). The suture between the maxillaries is about 

 5 inches long. This palatine part of the maxillary is convex transversely and smooth. 

 It is bounded above for the first five inches by a narrow (ecto-maxillary) groove, the upper 

 border of which projects, at first slightly, and then extends outward, forming behind the 

 groove a rough (ecto-maxillary) ridge (fig. 5, e), gaining both in transverse and vertical 

 extent or thickness until it reaches the middle of the naso-premaxillary plate, where it 

 swells into a convex tuberosity (fig. 5, (7), at the part answering to that in which the 

 vertical walls rise in Hyperoodon. Beyond the tuberosity the maxillary extends outward, 

 articulating first with the malar (20), then with the superorbital tract (]i) of the frontal, 

 sweeping upward, in a graceful curve, with that bone to join the base of the nasals. This 

 broad interorbital plate of the maxillary forms, with the similarly expanded nasal plate of 

 the premaxillary, a large and moderately deep semilunar cavity, perforated by the 

 (antorbital) canal and foramen, transmitting a branch of the second division of the 

 trigeminal (a). The cavity contracts and deepens forward, answering to that so marked in 

 the canal between the tuberosity {9) and the beginning of the premaxillary expanse, and 

 there opens the second canal (fig. 4, 6), continued from the antorbital one, for the chief 

 branch of the second division of the trigeminal, mainly answering to the suborbital or 

 antorbital nerve in land mammals, as in Physeter {Euphysetes) simus (" Indian Cetacea," 

 'Trans. Zool. Soc.,' vol. vi, pi. xiii ; Phocana drevirosfris {ih.,ip\Ax). The ectomaxillary 

 ridge (fig. 5, e) is grooved along the thick margin of its basal or hinder half. A narrower 

 groove, commencing three inches in advance of the foramen (5, fig. 4), extends forward 

 along the line of the maxillo-premaxillary suture to the anterior termination of the 

 maxillary. The whole of the rostral part of the maxillary extends outward, beyond the 

 subvertical plane of the side-wall formed by the premaxillary, and in a degree augmenting 



' 'Oss. Foss.,' torn, cit., pi. xxvii, fig. 3. 



