July 1. 1893.J 



KNOWLEDGE. 



121 



A N ILLU ST RATED 



MAGAZINE OF SCIENCE 



SIMPLY WORDED— EXACTLY DESCRIBED 



LONDON: JULY 1, 1893. 



CONTENTS. 



PAOE 



Tusks and their Uses. By R. Lydekkek, B.A.Cautab. ... 121 



The Story of e Eridani. By the Rev. T. D. Anderson, P. Sc. 124 



Galls and their Occupants— I. By E. A. Btjtlee ... 125 



The Tree Creeper. B\ IIakut F. Wittierby 128 



The Great Plains on the IVIoon. By A. C. Ranyard ... 129 



Notice of Bool< 130 



Science Notes 131 



Letters : — I. K. Holt ; .1, C. Kapteyn' ; J. jrArr.AiR I.hkastox 133 

 The Governmental Inquiry and the Field-Voles. By 



W. F. KiRBY, F.L.S., F.E.S 134 



Chemistry and Cuisine. By YAronAN CoRxit^H, M.Sc, 



F.C.S 135 



On some Recent Investigations of the Geology of the 



Punjab Salt Range. By C4. W. Bulman, M.A., B.Si-. 137 

 The Face of the Sky for July. Bj Heebbrt Sadler, 



F.R.A.S. 139 



Chess Column. By C. D. Locook, B.A.Oxon 139 



TUSKS AND THEIR USES. 



By R. Lydekkee, B.A. Cantab. 



ANY mammals, such as the elephant, hippo- 

 potamus, and walrus, are furnished with one or 

 two pairs of pointed conical or compressed teeth 

 largely exceeding all the others in length, and 

 to which the term "tusks" is usually applied. 

 Lions and wolves likewise have two pairs of somewhat 

 similarly enlarged teeth in the fore part of their jaws ; and 

 although these are proportionately smaller than in the 

 animals above named, it will be obvious that in popular 

 language it is difficult not to include them under the 

 same general title. Using, then, the term " tusks" for all 

 such enlarged simple teeth, it may be of interest to note 

 the groups in which these attain their greatest develop- 

 ment, and also endeavour to learn something regarding 

 their uses. An especial interest attaches, indeed, to the 

 subject, on account of the extreme beauty of many of 

 these teeth, and also from the circumstance that it is 

 these alone which yield the various descriptions of ivory. 



In a great number of instances such tusks comprise a 

 pair in both the upper and lower jaws, which are situated 

 immediately behind the front, or incisor teeth, and, 

 from their marked development in the dog tribe, are 

 scientifically designated canine teeth ; the name "eye-teeth " 

 being also not uufrequently applied to them in popular 

 language. Tusks of this sort are characterized by the 

 circumstance that the lower one on each side bites in 

 fi-ont of the upper one ; while the latter is always the 



M 



first tooth situated in the true upper jaw-bone, the incisors, 

 or front teeth, being implanted in a more anteriorly 

 situated bone known as the pre-maxilla. In any oi-dinary 

 carnivorous mammal, such as a lion or a wolf, the upper 

 tusk is considerably larger than the lower, although 

 neither project beyond the edges of the muzzle when the 

 jaws are closed. If we examine such tusks in a dried 

 skull we shall find that their roots (which, as in all tusks, 

 are simple) are completely closed ; thus indicating that 

 their growth ceased at a certain period of life. Moreover, 

 we may notice that the upper and lower pairs of tusks do 

 not abrade against one another to any marked extent, and 

 that consequently their summits are only subject to 

 the ordinary wear and tear necessarily undergone during 

 use. In many other mammals the form and structure of 

 these tusks is, however, very different. Take, for instance. 



Fia. 1. — Skeleton of Mastodon to show single pair of tusks 

 in upper ]ns\'. 



a wild boar, in which the upper tusks are short and curved 

 upwards, while the larger and more slender lower pair 

 abrade against their outer surfaces, and are thus worn to 

 sharp, cutting edges. Obviously such tusks, if they were 

 incapable of growth like those of the lion, would soon be 

 worn away to mere stumps and become useless to their 

 owners. To prevent this, the bases of the tusks remain 

 permanently open (as shown in Fig. 4), and contain a soft 

 pulp connected with the viiscular structures of the jaw, in 

 consequence of which the teeth continue to grow through- 

 out life ; their rate of growth thus keeping pace with that 

 of the abrasion to which they are subject. Tusks may 

 accordingly be divided into two classes, which we may 

 designate hollow and solid. The open tusks referred to 

 above are prevented from attaining any very great length 

 by the abrasion of the lower against the upper pair, but ir 

 other cases, as in those of the remarkable pig of Celebes 

 known as the babirusa (Fig. 2), no such abrasion takes 

 place, and both pairs then attain enormous dimensions, 

 projecting in this particular instance far above the upper 

 surface of the head, and the down-curving points of the 

 upper pair sometimes even penetrating the skull. A 

 babirusa may in fact be compared to a wild boar in which 

 one pair of tusks having been broken, the other continues 

 to grow without any abrasion by wear ; only that in thest 

 animals both pairs are thus developed. In the wild boar 

 and its allies the tusks — more especially those of the 

 lower jaw — are purely offensive and defensive weapons ; 



