MUSEUM OF COMPARATIVE ZOOLOGY. 83 



old, arc both females, but at this age the sexes probably differ but 

 little in osteological features, especially in those of the skull. In thcso 

 specimens the anterior or facial portion of the skull is but little developed 

 in comparison with the size of the brain-case. The muzzle is not only 

 excessively short (see Figs. 5-7, PI. II), but the orbital space is small, 

 and the postorbital cylinder is reduced almost to zero, the postorbital 

 processes being close to the brain-case. The zygomatic arch is hence very 

 short ; the zygomatic foramen is as broad as long, instead of being nearly 

 twice as long as broad, as in the adult. On the other hand, the brain-case 

 is exceedingly large, the greatest breadth of the skull being at the middle 

 of the brain-case instead of at the posterior end of the zygomatic arch. 

 As will be seen by the table of measurements of the skull already given, 

 the brain-case is nearly as large as in the adults, and the bones being 

 thinner, it must have a capacity about as great as that of the skulls of 

 the adult males and females, there being, in respect to this point, but 

 slight difference in the sexes. As the young advance in age, the anterior 

 portion of the skull, or that part in advance of the brain-case, greatly 

 elongates, especially the postorbital cylinder, and increases also in 

 breadth, the skull in a great measure losing the triangular form and the 

 narrow peaked muzzle characteristic of the young. The postorbital pro- 

 cesses also greatly change their form as they further develop, as shown 

 in the figures of Plate II. 



The limbs are also relatively much larger than in the adult, as men- 

 tioned by Quoy and Gaimard in respect to the Arctocephalus cinereus of 

 Australia,* which enables them to move on land with greater facility 

 than the adult, as the above-mentioned authors have stated to be the 

 case in the Australian species. 



It is not true, however, that the young of C. ursinus are devoid of under- 

 fill", as has been by some writers incorrectly stated.f 



Individual Variation. — The two males were both not only full-grown, 

 but quite advanced in age, though in all probability the crests of even the 

 older skull (Xo. 2922) would have been still further developed. The other 

 male (No. 2923) was somewhat younger, but already had the sagittal crest 



* Voyage de 1' Astrolabe, Zoologie, Tom. I, p. 89. 



f It may be added that .the young specimens above described had not fully shed their 

 milk teeth. The incisors appear to have been renewed, but both the first and second 

 sets of canines were still present (as shown in Fig. 5, PI. Ill, natural size), the permanent 

 ones being in front of the others. The three pre-molars of the first set have been re- 

 placed by the permanent ones, the first and second of which are already quite large. 

 The hinder or true molars are in one of the specimens but just in sight, and doubtless- 

 had not cut through the gum. In the other specimen they are a little more advanced. 

 The middle one is quite prominent; the first is much smaller, while the last or third true 

 molar is far behind either of the others in development. 



