xv BALEEN OR WHALEBONE 219 



am specially directing your attention, are, as I have mentioned, 

 in a more or less rudimentary state in the Cetacea; the baleen, 

 on the other hand, is an example of an exactly contrary con- 

 dition, but an equally instructive one, as illustrating the mode 

 in which nature works in producing the infinite variety we 

 see in animal structures. Although appearing at first sight 

 an entirely distinct and special formation, it evidently consists 

 of nothing more than the highly modified papillae of the 

 lining membrane of the mouth, with an excessive and cornified 

 epithelial development. 



The bony palate of all mammals is covered with a closely 

 adhering layer of fibro-vascular tissue, the surface of which is 

 protected by a coat of non-vascular epithelium, the former 

 exactly corresponding to the derm or true skin, and the latter 

 to the epiderm of the external surface of the body. Sometimes 

 this membrane is perfectly smooth, but it is more often raised 

 into ridges, which run in a direction transverse to the axis of 

 the head, and are curved with the concavity backwards ; the 

 ridges, moreover, do not extend across the middle line, being 

 interrupted by a median depression or rapht. Indications of 

 these ridges are clearly seen in the human palate, but they 

 attain their greatest development in the Ungulata. In oxen, 

 and especially in the giraffe, they form distinct laminae, and 

 their free edges develop a row of pointed papillae, giving them 

 a pectinated appearance. Their epithelium is thick, hard, and 

 white, though not horny. Although the interval between the 

 structure of the ridges in the giraffe's palate and the most 

 rudimentary form of baleen at present known is great, there 

 is no difficulty in seeing that the latter is essentially a 

 modification of the former, just as the hoof of the horse, with 

 its basis of highly developed vascular laminae and papillae, and 

 the resultant complex arrangement of the epidermic cells, is 

 a modification of the simple nail or claw of other mammals, 

 or as the horn of the rhinoceros is only a modification of 

 the ordinary derm and epiderm covering the animal's body 

 differentiated by a local exuberance of growth. 



Though the early stages by which whalebone has been 

 modified from more simple palate structures are entirely lost 

 to our sight, probably for ever, the conditions in which it now 



