250 DISCOVERY REPORTS 



With increasing age there is a general increase in smoothness and density of bone, 

 most noticeable perhaps in that of the cranium. 



In the youngest skulls the lambdoidal suture is only partly fused, but with increasing 

 age it is obliterated, as are the following sutures in the order given: sagittal, squamosal, 

 coronal and occipito-sphenoidal. There are developed very large and thick lambdoidal 

 crests and a less conspicuous sagittal crest which diminishes anteriorly and divides into 

 two low, bilaterally symmetrical ridges marking the temporal lines. 



As has been stated on p. 248, four age groups may be distinguished in each sex, and 

 the last undoubtedly comprehends all seals of the fourth year and over. 



In the following descriptions average measurements are given unless otherwise 

 specified, and figures in brackets indicate the number of specimens on which was based 

 the immediately succeeding figure : 



First year (5). Body length (2) 228-5 cm. ; skull length 332 mm. ; zygomatic width 

 172-6 mm.; alveolar length (4) 90-4 mm. 



The cranium is rounded and the anterior fonticulus may not be quite closed. The 

 lateral parts of the lambdoidal suture can be seen and the occipito-sphenoidal suture 

 is open; the sagittal suture is rather complex, the coronal sutures are unfused and the 

 squamosal bone is not fused to any other except the periotic and the tympanic. The 

 cheek teeth are crowded, the first in the upper jaw almost touching the canine. 



Second year (6). Body length (3) 253-7 cm.; ^^^^^ length 361-5 mm.; zygomatic 

 width 187-6 mm.; alveolar length 96 mm. The lambdoidal crests are beginning to 

 develop and signs of the sagittal crest give the dorsal profile a straighter line. The 

 lambdoidal suture is obliterated and the sagittal fused, as is also a considerable length 

 of the dorsal part of the coronal sutures. The squamosal suture is fused and the occipito- 

 sphenoidal may be partly closed but is still conspicuous. The cheek teeth are better 

 spaced. 



Third year (4). Body length 280-8 cm. ; skull length 381-5 mm.; zygomatic width 

 197 mm.; alveolar length 98-8 mm. The cranium is still smoother and better ossified, 

 the crests are larger and the lambdoidal crest developed to such an extent that the 

 dorsal profile of the skull may be almost saddle-shaped. The occipito-sphenoidal suture 

 is partly fused and there may be fusion of the maxillae and premaxillae on their palatine 

 faces. 



Fourth year and over (13). Body length (8) 289-4 cm.; skull length (12) 394-4 mm.; 

 zygomatic width 207-3 mm.; alveolar length (12) 101-9 mm. This final group contains 

 all the largest and most highly ossified skulls; the crests are invariably large and the 

 occipito-sphenoidal suture not only fused but usually obliterated. The premaxillae and 

 maxillae are fused in the alveolar part as well as the palatal. 



