286 DISCOVERY REPORTS 



eventually the palatine plates of the maxillae and of the palatines themselves fuse in 

 the middle line and the transverse suture between them closes. The pterygoids become 

 deeper and tend to approach one another below the level of the palate and the external 

 plates extend beyond the hamular processes. In the younger adults the jugal begins 

 to unite with the maxilla ; but it is only in the most completely ossified skulls that it 

 unites with the squamosal. 



In the adult the pre-orbital part of the skull becomes broad and massive in accordance 

 with the great development of the canine teeth and the upper third incisors. With 

 advancing age the bone surrounding the teeth, particularly the more anterior, and 

 forming their sockets, becomes thickened and rather cancellous, and some — frequently 

 front teeth — become broken or displaced, no doubt in fighting (Plates VIII, IX, X, 

 figs. 7). 



In the completely ossified state every suture is fused and almost all are obliterated, 

 so that the skull becomes a single mass of bone ; but only three of the thirty-one adult 

 male skulls available have reached this state. Of these skulls two are in the National 

 Collection and are 346 and 357 mm. in length respectively (the average length for the 

 entire series of thirty-one being 345 mm.), and the third which is in the Museum of 

 the Royal College of Surgeons is the largest skull I have seen — 382 mm. long. It is 

 27 mm. longer than the next largest, but in its proportions adheres closely to the 

 averages for the whole series of adult male skulls. Of these three skulls the diff"erence 

 between the smallest and the next in size is 1 1 mm. or 3-2 per cent of the smaller, the 

 difference between the second and the largest is 25 mm., 7-0 per cent of the second, 

 and between the smallest and the largest 36 mm. or 10-4 per cent of the smallest. 



It is quite clear from this series of skulls that full growth is not synonymous with 

 sexual maturity and that the size which may be attained is subject to considerable 

 variation. 



The most remarkable skull of an adult male is that in the British Museum (Natural 

 History), No. 33 5X, which came from the Falkland Islands. Although it is exceeded 

 in size by six others it is excelled by none in the development of the crests and tubercles. 

 Both of the upper canines and one of the third incisors are broken off ; it is the skull 

 of an aged animal. 



Female skull 



The series of female skulls numbers 34; of these 27 were collected between June 10 

 and August 10, and only those taken between these dates have been considered in 

 determining the annual stages. Two skulls of adult cows of unknown age collected in 

 November and January have also been retained for consideration. 



The female skull presents a series of changes which are analogous to but less pro- 

 nounced than those of the male, as might indeed be expected since the ultimate form 

 is much less specialized. The skull naturally retains at all times much of the juvenile 

 character, and this, combined with individual variability, renders less obvious the 

 differences between the age groups, which as in the male are six in number. 



FIRST YEAR. Total length 186-4 mm., 16-5 per cent of the body length; zygomatic 



