July 1, 1893.] 



KNOWLEDGE 



123 



mesoplodon, the tusks appear not only useless, but actually 

 harmful. In the whale in question, which is a rare species 

 from the southern seas, there is but one large strap-like 

 tusk on each side of the middle of the lower jaw, both of 

 these curving upwards and inwards over the snout, so as 

 to prevent the mouth from opening to its full extent. The 

 only possible use we could suggest of such a structure 

 would be to prevent the creature dislocating its jaw by 

 yawning ; but as other animals manage to get on without 

 such an arrangement, this is scarcely likely to be a solution 

 of the problem. It is more probable, indeed, that we have 

 here to do with another instance of ultra, or monstrous 

 development. 



Other examples of hollow or permanently growing tusks 

 occur among the hoofed mammals, other than the pigs, in 

 all of which these teeth are found only in the upper jaw, 

 and are developed chielly or solely in the males. Among 

 recent forms these tusks attain their gi-eatest development 

 in the little musk-deer of the Himalaya, where they are fre- 

 quently over three inches in length, and project considerably 

 below the lower jaw. In form they are sabre-like, and recall 

 the upper tusks of the feline carnivores, only bemg more 

 slender, and growing permanently. Similar but smaller 

 tusks are met with in the Chinese water-deer, in the Indian 

 muntjac, and the little deer-like 

 animals known as chevrotains. 

 The latter belonging to a totally 

 distinct group from the others, it 

 is evident that these scimitar-like 

 tusks have been independently 

 acquired in the two groups ; 

 while it is quite probable that 

 those of the musk-deer and 

 Chinese water-deer are likewise 

 of separate origin. With the 

 exception of the muntjac, in 

 which they are very small, all 

 these deer-like animals are devoid 

 of antlers ; and it is thus evident 

 that their tusks have been de- 

 veloped in lieu of those weapons. 



It is true, indeed, that the males of some of the antlered 

 deer have small tusks, but these are of no use for offen- 

 sive purposes, and are evidently organs in process of 

 degeneration. Moreover, in the hollow-horned ruminants, 

 such as oxen and antelopes, where the horns are per- 

 manent and generally present in both sexes, not a vestige 

 of tusks remains. 



Although the Asiatic 

 rhinoceroses have pro- 

 cumbent tusks of consider- 

 able size in the lower 

 jaw, none of the odd-toed 

 hoofed mammals, such as 

 horses and tapirs, have 

 upper tusks of any size. 

 In past times there were, 

 however, in North America 

 a group of somewhat 

 allied creatures known as 

 uintatheres, in which an 

 enormous pair of upper 

 tnsks, somewhat like those 

 of the musk-deer, was de- 

 veloped. Like those of 

 the latter, these tusks 

 grew permanently, and 

 they were also protected 

 the lower jaw, which was 



FiCr. 4. — Extremity of tlie 

 skull of II young Chinese 

 Water- Deer, with the base 

 of the tnsk exposed. (After 

 Sir V. Brooke.) 



Fig. 



—Extremity of the 

 of a T-'intathere. 



*ull 



by a descending flange of 



often deeper than in the figured example. As these 

 animals had front teeth only in the lower jaw, we have 

 here, therefore, another curious instance of the parallel 

 development of similar conditions in totally unconnected 

 groups. What use these creatures could have made of 

 their tusks is, however, not very clear, as in the living condi- 

 tion they could have projected but little below the lower jaw, 

 while they were too long to have been effectual when the 

 mouth was open. These uintatheres were also noteworthy 

 on account of having a number of bony projections on the 

 top of the skull, which in life may have been sheathed in 

 horn ; and it is not a little remarkable that another extinct 

 creature — Protoceras — belonging to the even-toed group 

 of hoofed mammals had a skull with very similar bony 

 projections and also similar upper tusks. 



Our last instance of animals furnished with per- 

 manently growing upper tusks is afforded by the reptilian 

 class, in which the extinct South African creatures 

 described many years ago by the late Sir K. Owen, under 

 the name of /^'((//wi/rfon, are thus armed. In these reptiles, 

 some of which attained gigantic dimensions, the jaws were 

 mainly sheathed in horn like those of the turtle ; the single 

 pair of tusks curving downwards and forwards from near 

 the middle of the upper one. Possibly these tusks were 

 capable of being employed when the mouth was open, 

 like those of lions or tigers ; but otherwise it is difficult to 

 see their use. Certain allied reptiles from the same for- 

 mations, known as anomodonts, had a full series of teeth, 

 with a large pair of tusks in the upper jaw, which may or 

 may not have been rooted, but are exceedingly like those 

 of certain carnivores. As these reptiles are not the direct 

 ancestors of mammals, we have thus evidence of the 

 acquisition of tusks in two distinct classes. 



As regards solid tusks, or those in which the lower end 

 is closed at a certain period coincident with the cessation 

 of growth, almost the only mammals, save the rhinoceroses 

 (where, as we have seen, there may be a forwardly-directed 

 pair in the lower jaw) and some of the marsupials, in 

 which they attain any marked development are the carni- 

 vores. Among these, the maximum size of tusks at the 

 present day is attained in the largf-r felines, such 

 as the Hon, tiger, and leopard. In these animals the 

 tusks are, however, never so much elongated as to bar the 

 front of the open mouth ; while very frequently their 

 tearing power is increased by the hinder cutting edge 

 being finely serrated. Their terrible effect in tearing and 

 rending the animals upon which these fearsome carnivores 

 prey is too well known to need further mention. During 

 the tertiary period there existed certain carnivores nearly 

 allied to the modern cats, but exhibiting a much greater 

 development of the upper pair of tusks, with a corre- 

 sponding reduction of those of the lower jaw. In these 

 creatures, which are known as machierodonts, or sabre- 

 toothed tigers, the upper tusks were greatly compressed 

 and flattened, with serrations on one or both cutting 

 edges ; their length in a species of the approximate size of 

 a tiger being upwards of seven inches. As in the 

 uintatheres, the anterior end of the lower jaw had a 

 descending flange to protect the end of the tusk. Mani- 

 festly, such enormous weapons would completely bar the 

 sides of the open mouth, and consequently they could not 

 be used in the manner of the tusks of a lion or tiger. It 

 is still more difficult to imagine that these animals could 

 have striick with their tusks projecting from below the 

 closed mouth ; and it would consequently seem that in 

 this instance also the tusks attained a development which 

 was harmful rather than advantageous — this con- 

 clusion being confirmed by the fact, for what it is 

 worth, that the sabre-toothed tigers have become totally 



