ME. W. H. FLOWER ON THE OSTEOLOGY OF THE SPERM-WHALE. 321 



The bones containing the organ of hearing have been figured by Camper* and 

 Owenf . 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 [Oica 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 petrosal J. 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 correspondmg 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 : — 



inolies. 



Extreme length 201 



Extreme breadth (across posterior part of orbital processes of frontals) 87 



Extreme height (top of occipital crest to bottom of pterygoids) ... 65 

 Length of rostrum (from tip to line drawn across bottom of antorbital 



notches) li'j 



Width of commencement of rostrum (inside antorbital notches) . . 61 



Width of rostrum at quarter distance from base, in straight line . . 58 



Right maxillary 23 



Left maxillary 24 



Eight premaxillary 5 



Left premaxillary 6 



Space between premaxillaries 4 



* Op. cit. plates xxiv., xxv., and xxvi. 



t Brit. Foss. Mammals, p. 526. Natural size, though stated bj' mistake to be half the natural size. 



t In the specimens figured by Camper and Owen this process has been broken off. 



