318 JtfR. W. H. FLOWER ON THE OSTEOLOGY OF THE SPERM-WHALE. 



ends abruptly in a narrow bifid extremity on a level with the posterior margin of this 

 passage ; the right continues onwards, and, passing the blow-hole, expands into a thin 

 broad plate, applied to the anterior surface of the frontal, and reaching to within 6" 

 of the summit of the crest. 



On the left side, corresponding to this plate, overlying the frontal, and resting below 

 on the top of the ethmoid, is a large, flat, very thin, loose lamina of bone (n). Its lower 

 edge is thicker and rounded ; but it terminates above by delicate irregular digitations. 

 This measures 14" in breadth, and rather more in height; but a considerable part 

 appears to be wanting from its upper edge in the adult specimen, having probably been 

 lost in maceration, or perhaps never completely ossified. It is more perfect in the young 

 skull, and partially united to the frontal (see PI. LVII. fig. 1). This I take to be the 

 left nasal bone, as it corresponds in situation and relations Avith that bone in the 

 Hyperoodon, although, in common Avith the other bones of the crest, it is excessively 

 flattened out. 



In none of the skulls examined could any trace of a right nasal bone be seen. Its 

 development appears to be interfered with by the ascending plate of the premaxillary ; 

 or it is possible that it is concealed beneath this. In the foetal skull in the Museum of 

 the College of Surgeons, described by Owen and Huxley, the left nasal is absent ; pro- 

 bably it was not ossified at this early age. 



In front of the blow-holes the upper surface of the skull is comparatively flat, 

 although still rising in the greater part of its extent fi-om the centre towards the sides. 

 This region is formed by the premaxillaries, in the shape of a pair of long narrow bands 

 of varying width, with very sharp edges overhanging the median vomerine groove, but 

 mainly by the greatly developed rostral portion of the maxillaries. These bones are very 

 massive, and expand in width in front of the deeply marked antorbital notch (a on). 

 Their flat upper surface is formed of a very thin plate of bone of remarkably dense and 

 brittle texture. Their internal structure is cancellous, the large distinct cells, almost 

 like those of a honeycomb, being filled in the natural state with oil. 



The infraorbital foramen (if) is represented by a fissure 10" in length, and 2" in 

 breadth, placed between the blow-hole and the antorbital notch, but nearer the latter. 

 This gives passage to the great branches of the fifth nerve destined to supply the enor- 

 mous upper lip and face. 



In the right premaxillary, 15" in front of the blow-hole, is an oval fossa, 3" in 

 length, leading into a canal which runs outwards, and communicates with that leading 

 to the infraorbital foramen. There is no corresponding opening on the left side. 



Lateral surface of the Skull (PI. LV.). — ^The temporal fossa is very small, though 

 scarcely so much reduced as in Hyperoodon. It is especially compressed from before 

 backwards, lying deeply between the great projecting masses formed by the squamosal 

 behind and the orbital process of the frontal in front. Above, it has not any distinct 

 limiting ridge as in Hyperoodon and most Dolphins, but passes almost insensibly on to 



