13 



Sydney 

 Skeleton. 



Under jaw 

 from Twofold 

 Bay, pre- 

 sented by 

 B. Boyd, Esq. 



Under jaw 

 presented by 

 G ^" 

 Esq 



Length of lowei' jaw in straight line.. 



Length of symphysis 



Length of series of dentary alveoles... 

 Distance between outer edges of the 



articular condyles 



Height of the mounting branches of 



the lower jaw 



Width of jaw where the symphysis 



begins 



Number of teeth 



Ft. In. 



42 



42 



42 or more 



According to Mr. Gray, who probably, witb Beale, took John 

 Hunter as his authority for the assertion, not only the number 

 of teeth A'aries according to age, but the length of the lower jaw- 

 appears to increase in front, so that in the older specimens the 

 symphysis is more, and in the younger ones less than one-half of 

 the entire length of the under jaw. In our three Sydney under 

 jaws there can be no doubt that the disproportion between the 

 length of the symphysis and half length of the entire jaw goes 

 on increasing according to the size of the animal ; but all three 

 have their symphysis longer than half the length of the under 

 jaw. It is also certain that the inspection of the greatest under 

 jaw in the Sydney Museum, may induce one to think it possible 

 that, as Mr. Gray says, the symphysis increases with age in a 

 greater proportion than the whole length of the lower jaw. By 

 the way, I may remark, that this largest specimen also appears 

 to exhibit more than forty-two dentary alveoles or sockets. "We 

 thus have Johu Hunter's position illustrated, that " tJie exact 

 number of teeth in any species of sperm ivTiale is imcertain ;" since 

 as the posterior part of the jaw becomes longer with age, the 

 number of teeth in that part increases, and the sockets become 

 shallower and shallower, until, in the end, there is only a slight 

 depression to mark their place. 



