158 BULLETIN 99;, UNITED STATES NATIONAL MUSEUM. 



same age. The latter present a striking case of definite structural 

 modification of the skull by habit. This is accompanied by a change 

 in color, the nature of which is equally definite, but the cause of which 

 is less easy to understand. 



The Hons brought from the relatively dry highlands of East Africa 

 became darker in color with each successive moult. The degree of 

 color change was therefore in direct relation to the period of life in 

 Washington. The effect of five years of such life has been to change 

 the color of living examples of Fells leo massalca from the normal 

 pale grayish-buff color of the race to a much darker color very much 

 resembling that of Felis leo nyimzse, the lion of the more humid 

 Victoria Nyanza region. The cause of this color change is unknoN\'n, 

 though humidity is probably a factor of some importance. Captive 

 lions also develop much finer manes and at an earlier age than do 

 wild animals of the same kind. 



Of greater interest in the study of the MciMillan lions compared 

 with wild examples from the same region are the modifications in 

 the skulls. In all adult captive animals the skulls have a definite, 

 uniform shape, differing from those of wild-kiUed lions in a number 

 of conspicuous characters. They are broader and shorter, more 

 massive and bulk}^, and exhibit abundant relative differences which 

 would be instantly accepted as of "specific" value in wild animals. 

 The obvious reason for the peculiarities of the zoo-reared individuals 

 is that the principal muscles opera tmg the jaws and neck (those 

 muscles used by a wild lion in maulmg and killing game, biting, 

 gripping, and shaking) have had so little work to do that the}^ liave 

 had relatively little influence in moulding the shape of the bones to 

 which they are attached. In a wild lion which habitually kills 

 quantities of heavy game, these muscles are much used, and in a 

 normal way they mould the growing skuU. 



The most conspicuous peculiarities of the McMillan lion skulls, 

 and of other zoo-reared lions as well, are the greater (relative and 

 actual) zygomatic breadth, the large rostra, and the great distance 

 across the base of the skull at the mastoids. While actually measur- 

 ing less in condylobasal or greatest length than many of the wild 

 massaica skulls of equal age, they have a far greater zygomatic 

 breadth than any, averaging about 30 millimeters more in males, and 

 20 mUhmeters more in females. (See detailed measurements, pages 

 166-167, and plates 52-54.) The dift'erent regions of tlie skull may 

 be compared in detail: 



Regions oi attachment of the masseter mwsfZ^. —Contrary to the usual 

 textbook definition of its function, the masseter muscle unquestion- 

 ably furnishes the chief gripping power; it is the one most exercised 

 during use of the canine and incisor teeth. ^Vliile there is intimate 

 relationship between the functions of the masseter and temporal 

 muscles, and the two masses are actually connected, each nevertheless 



