MR. W. H. FLOWER ON THE OSTEOLOGY OF THE SPERM-WHALE. 321 
The bones containing the organ of hearing have been figured by Camper* and 
Owen}. They are remarkable for their small size, compared with that of the cranium. 
Not only are they much inferior to those of the true Whales, but actually less than 
those of the common Killer (Orca gladiator). In general conformation the tympanic 
and petrosal bones do not differ from those of other toothed Whales; their principal 
peculiarity is the development of a large mass of curiously laminated bone from the 
posterior and outer end of the tympanic, close to its attachment to the petrosalf. This 
is 6" long, and thicker at its outer than at its attached extremity. It is composed 
of a large number of distinct thin plates, only held together by their common attach- 
ment to the tympanic. The whole mass partly overlaps and embraces the hinder edge 
of the squamosal, and partly fits into a groove between the latter and the exoccipital, 
and serves to attach the petrotympanic much more firmly to the cranium than is the 
case with other Toothed Whales. It evidently corresponds to the strong tenon-like 
process of corresponding situation and function in the Whalebone-Whales. The con- 
tiguous edge of the squamosal has a laminated character, the ridges and grooves on its 
surface exactly fitting into those of the appendage to the tympanic. 
The petrotympanic is, as in most Dolphins, further steadied in its place by a long, 
narrow, flat process, which runs out from the squamosal downwards and backwards 
immediately in front of it. The length of the tympanic is 2'"6, the greatest breadth 
of the united tympanic and petrosal is 2""9. As might be expected, there is scarcely 
any appreciable difference in the size or form of these bones in the young and the adult 
animal. 
The principal dimensions of the cranium are as follows :— 
inches. 
Extreme length . .. . : : 201 
Extreme breadth (across Sane hark oe Gaia processes sof feontals) 87 
Extreme height (top of occipital crest to bottom of pterygoids). . . 65 
Length of rostrum (from tip to line drawn across bottom of antorbital 
iGOILENES) ne Se Se to els aaeprmece tan NG 
Width of commencement of rostrum “Gastad vtrtital nbEeheay one lal 
Width of rostrum at quarter distance from base, in straight line . . 58 
Le aig an. an ene amc aarmar aren (nese. 
isis ELC FNS 7d ll ie epee eh rane merit me | SST ee. 
EeOPGRMECHIASANAL YS Ne ee teehee ego. ae Ngee das mee 5 
Topi gies lena ile Samal dledes meats Me tanertaatt pear eater hep wine We Sh Oe 6 
Space between premaxillaries . . . . .... =. --. - 4 
* 
Op. cit. plates xxiv., xxv., and xxvi. 
Brit. Foss. Mammals, p. 526. Natural size, though stated by mistake to be half the natural size. 
In the specimens figured by Camper and Owen this process has been broken off. 
ho i 
