DE, J. MUEIE ON THE ANATOMY OF THE SEA-LION. 



507 



They apply to the skull figured by me in PI. LXXVII. tigs. 16, 17, which is that 

 numbered 39G8, Cat. Coll. Surg. Besides the points here displayed in palatal views, a 

 comparison of the crania in the accompanying PI. LXXVII. further bears out state- 

 ments concerning said differentiations l . 



g. Progressive Cranial changes. — Although writers previously had incidentally ad- 

 verted to an alteration in the form of the skull with age in some of the Eared Seals, yet 

 no one has so forcibly pointed this out as Dr. Gray 2 . In one of his papers on the 

 Otariadce he justly remarks 3 : — "The skull of these animals changes so much in form 

 as the animal arrives at adult and old age, that it is not always easy to determine the 

 species by it, unless you have a series of them of different ages and states to compare." 

 So much do the parietal crest and other osseous prominences shoot forth in the 

 Sea-bear or Great Sea-lion of some travellers (Otaria jubata), that between young and 

 old specimens changes as great and characteristic as obtain in the cranium of the 

 Gorilla occur in them. 



In tracing the development of the skull of this species of Otaria, I have had the 

 advantage of comparing side by side a large number of both sexes and various ages. I 

 tabulated a series of proportional measurements of the relative growth of different 

 regions, but refrain from introducing the table in this place. Instead I have illustrated. 

 in Series PI. LXXVII., examples of five different stages of the development, to each of 

 which I append remarks. My figures have been drawn to a uniform scale, quarter 

 natural size ; I nevertheless subjoin, in inches and tenths, the absolute length, breadth, 

 and height of each, for greater precision. 



Crania of Otaria jubata. 



1st stage. 



15 to 20 



days. 



2nd stage. 



Yearling. 



3rd stage. 

 d ad. (nearly), 



2 ad. 



4th stage, 

 c? old. 



5th stage. 



6 very 



old. 



Nos. in Cat. Coll. Surg., except sp. 3rd column 



Greatest length, premaxilla to condyle 



Greatest breadth 



Greatest height, without mandible line cuttin 

 mastoid 



E } 



3971c. 

 6-5 



3-9 



3-6 



3971 b. 

 8-5 



4-0 



4-0 



Z.S.sp. 

 10-6 

 6-5 



4-0 



3968. 



I L-0 



5-8 



3971 a. 

 12-8 

 7-5 



6-0 



3971 e. 



14-:; 

 9-4 



8-2 



First stage. In the young skull of a few weeks old the brain-region is in prepon- 



ridges into a parietal crest, nor any considerable development of the occipital ridge. The boundary of the 

 large mastoid is well shown in this skull, together with the share which the paroccipital takes in this rough 

 muscular ridge external to the petrosal. The middle surface of the basioccipital is less carinate than in the 

 male. The entry of the carotid canal in the petrosal is more distinct from the jugular vacuity. The broad 

 superorbital processes of the frontal are less angular. The canines and external incisors of the upper jaw are 

 smaller in comparison with the molars. The first and second incisors have bifid crowns. The angle of the 

 lower jaw is produced and bent inwards more than in the male." 



1 I may also refer to a most valuable communication " On the Eared Seals," by Mr. J. A. Allen, Bull. Mus. 

 Comp. Zool. Camb. T. S. vol. ii. no. 1 (1870-71), wherein the author, with occasionally sweeping criticism, has 

 most adroitly woven together many facts concerning sexual variation and changes of the skull in the Xorth- 

 Pacific species. 



2 P. Z. S. 1859, p. 360, and Cat. of Seals and Whales in B. M. :; Ann. & Mag. Nat. Hist. 1868, i. 100. 



