232 Bulletin American Museum of Natural History. [Vol. XXII, 



teeth, the male exceeds the female (in the average) by about 4 to 5 

 mm. in the total length of the skull, while in the average, in strictly 

 comparable middle-aged skulls of the two sexes, the male exceeds 

 the female by about 6 mm. (about 4.4 per cent.) of the total length 

 of the skull. In other respects, as regards size and proportions, 

 there are, with the exception soon to be mentioned, no noteworthy 

 differences, the middle-aged male skull exceeding that of the female 

 in nearly all its dimensions proportionately with the difference in total 

 length. There is no difference in the length of the upper molar series, 

 nor in the size of the individual teeth. 



In the male, however, the upper canines are two to three times 

 the size of these teeth in the female, with a markedly greater difference 

 in the size of the lower canines, which in the male are about five times 

 larger than in the female. A corresponding increase in the stoutness 

 and breadth of the rostrum and in the development of the lower jaw 

 is of course entailed in the male by the excessive enlargement of the 

 canines, which strongly recall the great development of these teeth 

 in the pigs and peccaries. 



In old age, however, the male skull becomes greatly specialized 

 as compared with that of the female of corresponding age, or with 

 that of the middle-aged male. At the stage when the entire milk 

 dentition is still in situ, and m 1 has become functional, the skulls 

 of the two sexes are practically indistinguishable. By the time the 

 complete permanent dentition has been acquired, the sexual difference 

 in size has become well-marked, and the very different character 

 of the canines leaves no question as to the sex of the specimen. Other- 

 wise than in size and the character of the canines, the skull of the 

 young adult or middle-aged male does not differ from that of the 

 female. Following this middle-age stage, the development of old age 

 characters begins to differentiate the skull of the old male from that 

 of the young male, and still more markedly from that of the female. 



These old age characters are the development of occipital and 

 sagittal crests and postorbital processes, and a marked constriction 

 of the postorbital region of the skull. The teeth also become greatly 

 worn, in some cases little but the roots remaining; but this feature 

 is, of course, common also to very old females. The beginning of 

 the development of the sagittal crest is about coincident with, or 

 slightly precedes the first perceptible wearing of the tubercles of the 

 teeth, and its growth thence continues as long as the animal lives, 

 in very old animals reaching a height of 7 to 9 mm. Coincidently 

 with the development of the crest the constriction behind the orbits 



