THE SOUTHERN SEA LION 



289 



while the occipital segment is completely fused and the suture between the basi-occipital 

 and the basisphenoid disappears : this change has usually occurred in the male by the 

 second year, but in the female is a ready means of distinguishing between the third 

 year stage and its predecessor (Fig. 7^; Plates XI, XII, XIII, figs. 3). 



FOURTH YEAR. Total length 2247 mm., 157 per cent of the body length; zygomatic 

 width 1 17-5 mm., 52-3 per cent of the total length; hamulo-premaxillar length 

 141 mm., 627 per cent of the total length. The cranium is still more markedly flattened 

 and the whole skull is definitely more massive. The interparietal and parieto-frontal 

 sutures have increased in complexity, and the temporal line is beginning to approach 

 the sagittal. There is a relative enlargement of the pterygoid, which is associated 

 with a straightening in a vertical line of the suture between the pterygoid and the 



,/ ^-^^ \ c , 



ha ha 



Fig. 7. Pterygoid regions of three skulls of female sea lions. 



a. Third year, specimen No. 1061. b. Fourth year, specimen No. 1023. c. Fifth year, specimen No. iioo. 

 In each figure: ha = hamular process; pa = palatine hone; pt = pterygoid bone. 



palatine. The hamular processes are still comparatively slender and the palate begins 

 to assume the laterally contracted form characteristic of the adult (Fig. 76; Plates 

 XI, XII, XIII, figs. 4). 



FIFTH YEAR. Total length 231-0 mm., being 14-8 per cent of the body length; zygo- 

 matic width 128-3 mm. and hamulo-premaxillar length 152-3 mm. which are re- 

 spectively 55-5 and 65-9 per cent of the total length of the skull. The skull is now 

 approaching the adult character; in some specimens the occipital and sagittal crests 

 begin to appear and the temporal lines almost meet anteriorly. The zygomatic arch is 

 markedly more massive and the palate displays the narrow, concave and elongated form 

 of the adult. There is an increase in the relative length of the facial part of the skull, and 

 the downwardly directed plates of the pterygoids show a still further increase in size, 

 while their junction with the palatines is almost quite straight. The hamular processes 

 are more oblique, and in their increased length approach the fully adult condition 

 (Fig. 7^ ; Plates XI, XII, XIII, figs. 5). 



SIXTH YEAR, AND OLDER. Total length 254-9 mm., H'2 per cent of body length; 



