654 UNGULATES. 



upon the number of points at which the base of the gelatinous 

 (dentinal) pulp is attached to the bottom of the capsule ; and that 

 the interspaces of these attachments constitute the under part of 

 the crown or body of the tooth, the attachments themselves 

 forming the first beginnings of the fangs. True to his hypothesis 

 of the formation of the dental tissues by excretion he says(l) 

 that the elongation of the fangs is produced by two circumstances : 

 first, the progressive elongation of the layers of osseous substance 

 (dentine) which force the tooth to rise and emerge from its socket : 

 secondly, the thickening of the body of the tooth by the addition 

 of successive layers to its inner surface, which, filling up the 

 interior cavity, leaves scarcely room for the gelatinous pulp and 

 forces it down into the interior of the roots. 



This puUing up of the fang on the one hand and squeezing 

 down of the pulp on the other, are forces too gross and mecha- 

 nical to be admitted for a moment in a physiological explanation 

 of the growth of the root of a tooth or of any other brganized 

 product; such modes of explanation were nevertheless inevitable 

 consequences of the adoption of the excretion-theory of dental 

 development ; and their proposition by the great Anatomist recalls 

 the analogous attempts of the great Master of Physical Science 

 to explain some of the phenomena of polarized light in the terms 

 of the ' emission-theory.' 



But Newton, whatever difficulties of explanation his theory 

 entailed upon him, is accurate as to the facts or phenomena : 

 Cuvier, however, is compelled by his hypothesis to deny a matter 

 of fact. (2) The cement (cortical), being, according to him, an 

 excretion from the internal layer of the capsule, could only be 



(1) " Ces racines et les pedicules qui leur servent de noyaux s'alongent ensuite par deux 

 raisons : d'abord les progres des lames de substance osseuse qui, s'alongeant toujours, forcent la 

 dent h s'elever et a sortir de I'alveole ; ensuite I'epaississement du corps de la dent par la forma- 

 tion des couches successives qui, en remplissant le vide interieur, n'y laissent presque plus de 

 place pour le noyau gelatineux, et le refoulent vers I'interieur des tubes des racines." Annales 

 du Museum, rai, 1807, p. 108, Ossem. Fossiles, 1834, p. 527- 



(2) " II ne se produit point d' email ni de cortical sur les racines, parce que la lame interne 

 de la capsule, qui a seule le pouvoir de secreter ces deux substances, ne s'etend pas jusque Ik." 

 loc. cit. (1807) p. 109 ; 1834, p. 527. 



