639 



venous sinuses terminating above the foramen magnum are present in this as in the preceding 

 skulls of the same species. The basioccipital is also perforated by a similar venous sinus near 

 its middle part. The petrosal is excavated by a deep but narrow cerebellar fossa ; a long 

 groove or notch upon its upper surface leads to the meatus auditorius internus : the petrosal 

 is, as it were, bent upwards upon this groove. The tympanic bulla supports the under part 

 of the petrosal like a capsule. The tympanic cavity is divided into two chambers, one above 

 the termination of the meatus externus, the other beneath and internal to it. The carotid 

 canal perforates the tympanic internal to this part of the chamber. 



In the anterior section the oblique expanded inner termination of the meatus auditorius is 

 shown, and its relative position to the small suprameatal and large infrarneatal divisions of the 

 tympanic cavity. The Eustachian groove commences from the angle between those divisions, 

 and grows deeper and wider until it forms the canal at the fore part of the tympanic bone. 

 The rhinencephalic fossa is divided by a strong and sharp crista galli. The frontal bones 

 form an unusually small proportion of the cranial cavity : they are extensively overlapped 

 posteriorly by the parietals. 



Presented by the Ven. Archdeacon Williams. 



3923. The anterior portion of the upper jaw of the great Proboscis-Seal (Cystophora 

 proboscidea). 



The external walls of the alveoli of the canines and molars of the right side of both jaws 

 have been removed ; showing the great size of the root as compared with the enamelled crown, 

 the longitudinal prominence on the outer side of the crown of the upper canine, the progress- 

 ive diminution in the length of the upper molars, and the near equality in the length of the 

 lower molars : the roots of the teeth converge slightly towards their implanted extremities in 

 both series. 



These jaws are from the original specimen brought to England by Lord Anson from the 

 South Seas, in 1 744. See Anson's ' Voyage round the World,' p. 1 22, pi. 1 9, where the spe- 

 cies is called the " Sea Lion." 



Mus. Brit. 



1 



3924. The right upper canine of the Cystophora proboscidea. Hunteriau. 

 39:25. The right upper canine of the Cystophora proboscidea. Hunteriau. 



3926. The right upper canine of a somewhat older individual of the Cystopkora pro- 

 boscidea. Presented by Sir William Blizard, F.R.S. 



3927. The right upper canine of a younger specimen of the Cystophora proboscidea. 



Hunterian. 



3925. The left upper canine of the Cystophora proboscidea. Purchased. 



