OF THE RED CRAG. 



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tion has abruptly proceeded to convert the prefrontal cartilage into a dense mid- 

 tract of bone (fig. 4, 14') of a petrosal texture, and of unusual breadth, viz. 2 inches 

 9 lines, at about three inches in advance of the part w^here this ossification gains the level 

 of the premaxillaries. Prof. Gervais's figure shows the ossified prefrontal (his ' vomerine') 

 tract to rise and expand with similar abruptness in the type Ziphius cavirostris (cut, 

 fig. 1, 14')- From its broadest part, in Ziphius indicus, the mid-tract contracts, at first 

 gradually, then more suddenly and unsyrametrically ; the sutural fissures between it and 

 the premaxillaries (22) becoming shallower and widening into grooves, which demonstrate 

 at their bottom the complete coalescence of the prefrontal and premaxillary elements of the 

 rostrum. The grooves are continued to the end of the rostrum, and indicate the share 

 contributed there by those bones respectively. 



The side walls of the rostrum, formed by the premaxillaries (22), rise almost vertically 

 from the sutures with the maxillaries (21), and terminate above in a border, which is 

 obtuse for the first six inches, from the end of the snout backward ; it then becomes a 

 sharp margin bent inward, so as partly to overlap the raid-tract (14') • The inward 

 inflection becomes greater, and the border is again thickened and also roughened where 



Fig. .5. 



Ziphius indicus, V. B. l-8th nat. size. 



it arches over the part of the cavity left by the unossified part of the prefrontal (14). The 

 same modification characterises the type-specimen of Ziphius cavirostris (fig. 1, 22-^). 



is an enlarged upper view of part of the same skull (' de la plage des Aresquiers'), as the upper view of the 

 entire skull given in figure 2 of pi. xxxix ; while figure 2 of plate xxxviii is a view of the upper surface of 

 part of Cuvier's specimen (' de la plage de Fos.'), of which a side view of the whole specimen is given in 

 fig. 3, pi. xxxix, of the ' Zool. et Paleont. fran9aises.' 



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