20 MR ROBERT B. THOMSON: SCOTTISH NATIONAL ANTARCTIC EXPEDITION: 



observed. The occipital bone presented occipital crests which were well marked, as also 

 were the par-occipital processes. Two well-marked supra-occipital venous foramina 

 were to be noticed in the middle line of the occipital squama. The condylar articular 

 surfaces were highly convex and approached close to each other on the inferior aspect 

 (7 mm.) ; above, they were distant 41 mm. 



The basi-occipital was quadrilateral in form, Hat and thick. The tympanic bulla 

 was smooth and rounded. The carotid canal was separated from the jugular foramen 

 by a thick bar of bone. In the interior of the skull the tentorium cerebelli and falx 

 cerebri were partly ossified. 



In the female skull the nasal bones were not ankylosed, and measured 55 mm. long. 

 The distance between the anterior edge of the nasals and the premaxilla was 20 mm. on 

 right side, 18 mm. on left. 



The Lower Jaw. 



The body was long and somewhat slender, due to small size of teeth, with lower 

 border slightly incurved. The ramus formed with the body a moderate angle and 

 possessed a well-marked sub-condyloid process. The condyle, which was convex and 

 elongated transversely, was separated from the coronoid process by a shallow sigmoid 

 notch. The coronoid process was short and pointed. 



Dentition. 



The dentition of the Ross seal is remarkably feeble, and varies more especially with 

 regard to the number of post-canines. Dr E. A. WILSON, in vol. ii. of Natural History 

 of National Antarctic Expedition, 1907, states : "The food of the Ross seal consists 

 mainly of soft-bodied cephalopods, and to this end has developed the incisors and canines 

 into needle-pointed recurved hooks of great delicacy and has allowed its post-canines to 

 degenerate. The gums presumably can manipulate such food as well as could molar 

 teeth, and so we find in some cases the post-canines are small and insignificant, whereas 

 in others they are loose and useless, and occasionally absent altogether." He also gives a 

 complete table of the dentition of all the Ross crania which have been brought home, 

 and which shows the great variations one meets in the dental formula. To this list I 

 would add the formulae of the two specimens of the Scotia : 



No. 2. Female, 2 - L 5 



No. 43. Male, 



2. 1. 5 



2. 1. 5 



2? 1. 5? - 



No. 2 skull presents for examination a perfect set of teeth, both upper and lower. 

 The upper incisors are more powerful than the lower, but both present, like the canines, 

 the well-marked recurved, needle-pointed character. The post-canines are recurved 



(ROY. BOC. EDIN. TRANS., VOL. XLVII., 190.) 



