FOSSIL REMAINS. 63 



teriuiiiatious ; but other specimeus, of the base and iutermedi- 

 ate portions, have come to light. Throughout its length," j\Ir. 

 Lankester continues, " which in some examples must have been 

 fully three feet, the tusk is slightly ciu'ved 5 but in those which 

 appear to be fully grown the curve is considerably greater 

 towards the terminal point, the direction of the curve probably 

 giving the tusk, if its Pinnigrade affinities be established, a 

 retroHected position, as in the Binotlierium. The Crag tusk 

 is very much compressed laterally, so that its transverse sec- 

 tion has an elliptical 'outline, whilst that of the Dinotherlum- 

 tusk is nearly circular. The amount of lateral compression 

 is, however, extremely variable, as it is also in the living Wal- 

 ruses; the amount also of the lateral as well as the antero- 

 posterior flection of the tusk appears to vary, as in the recent 

 Trichecus, the variabilitv of which in the size and form of its 

 tusks is well known. A single large furrow on the outer sur- 

 face, two on the inner, and one on the inner curved margin, ex- 

 tend along the whole length of the tusk in many specimens, 

 exactly similar to those on some tusks of Walrus ; but in both 

 the recent and fossil specimens they are subject to much varia- 

 tion, in their major or minor development. I^o ax^pearance of any 

 wearing of the point of the tusks by use during life is observa- 

 ble ; and indeed the greater backward curvature of that part 

 seems to result from its freedom from usage, since in the Walrus 

 the point of the tusk is rapidly worn away, which of course 

 checks any tendency to curvature which might become appar- 

 ent if the tusk were not useti against such hard substances as 

 rocks and blocks of ice. 



" From an examination of the general contour and form of the 

 tusks, without regard to their substance or structure, one would 

 unquestionabl}^ be led to regard them as belonging to an animal 

 similar to the existing Walrus, inasmuch as it is in this animal 

 alone that this form of tusk, Avith its longitudinal furrows, great 

 length, and gentle curvature, is found." 



After describing in detail the structure of these fossil tusks, 

 as shown in sections and as revealed by 'the microscope, Mr. 

 Lankester further observes: '"^Jn its microscoi)ical structui-e, 

 the dentine of the fossil tusks presents a comx)lete resemblance 

 to that of the Wakus.* .... The dentinal tubes are very 



* TlieJr ruicroscoiical structiu-e, as well as external form, are illustrated 

 by umneroiis ligtires, forming plates x and xi, acconij)auying Mr. Laukes- 

 ter's paper. 



