284 



DISCOVERY REPORTS 



+ 



YEAR OF 

 2nd , 3rd , 



AGE 

 4th 



5th ,6th o» over 



330- 



310 



290 



270- 



250 



230- 



210 



BODY LENGTH [cm] 

 SKULL LENGTH [MM] 



HAMULO- PREMAXILLAR LENGTH [MM] 



ZYGOMATIC WIDTH [MN/1] 



The skull of the third year is 239 mm. long, 157 per cent of the body length; 

 zygomatic width 129-1 mm., 54 per cent of the skull length; and hamulo-premaxillar 

 length 156-4 mm., or 65-4 per cent of the skull length. 



This stage has a more massive skull and the profile of the cranium is beginning to 

 be flattened. The first sign of a ridge appears at the posterior edge of the temporal line, 

 which is more strongly marked and 

 still nearer the vertex than in the Ist 



preceding stage; the supra-occi- 350- 

 pital begins to fuse with the 

 parietal bones. The canines are 

 now the longest of the teeth (Plates 

 VIII, IX, X, figs. 4). 



By the fourth year the length 

 is 270-6 mm., being 15-7 per cent 

 of the body length; the zygo- 

 matic width is 143-2 mm., 52-9 per 

 cent of the skull length ; and the 

 hamulo-premaxillar measurement 

 is 181 -4 mm., 67-0 per cent of the 

 skull length. 



The juvenile appearance has 

 been lost and indications of the 

 eventual form of the skull begin 

 to appear. The supra-occipital and 

 the parietals are completely fused 

 and the temporal lines almost meet 

 in the middle line; they are separ- 190- 

 ated only by a slight bony ridge on F'S- 3- 



each frontal, the beginning of the 

 sagittal crest. The canines are naturally still larger and the incisors show signs of wear 

 (Plates VIII, IX, X, figs. 5). In this stage and in all those which precede it the nasal 

 part of the skull has a curved profile and the dorsal surface of the nasal bones is easily 

 seen from in front. 



In the FIFTH, SUB-ADULT, YEAR the skull has a length of 308-5 mm., 14-6 per cent of 

 the body length; with a zygomatic width of 175-5 ^t^-, and hamulo-premaxillar length 

 of 214-5 mm., 69-5 per cent of the skull length. 



Although it is much less massive than in the adult the skull of this stage is definitely 

 suggestive of the ultimate form; the dorsum is nearly straight, and instead of being 

 curved down towards the front, the nasals are now nearly in a straight line with the 

 dorsum, with the result that the front edges and not the upper surfaces of the nasals 

 are presented towards the front. There are distinct but not largely developed occipital 

 and sagittal crests and only the latter separate the temporal lines, so that the jaw 



230 



210 



190 



170 



150 



130 



no 



Male sea lions. Increase in measurements 

 during growth. 



