206 ON THE lOS-SIL BOXES OF PACHYDERMATOUS QUAURUIM DS. 



it; so we may change its direction by gentle pressure. This is an ex- 

 periment which succeeded vvitli our second elephant : its tusks approxi- 

 mated so as to impede the motions of its trunk ; they were gradually 

 separated by means of an iron- bar, the middle of which was formed 

 like a screw (en vis), and which was lengthened at pleasure. Every 

 one knows that dentists do the same thing in a small way with children, 

 for teeth which have but one root. 



The successive layers of which ivory consists, leave but few traces 

 on the section of a recent tusk : but here the fossile tuskt aid us much 

 better in learning the structure of the parts. The tusks decomposed 

 and altered by remaining in the ground, ai-e arranged in conical thin 

 lamellae, all enveloped the one in the other, and thereby show what 

 was their origin. 



No bone properly so called is disposed in this way, Sloane is, I 

 think, the first who made this remark. 



Incisions made on the surface of a tusk, are never filled ; they dis- 

 appear only according as the tusk is used by friction. 

 : It is true, we sometimes see balls in the interior of ivory, without 

 seeing the hole through which they entered. 



Our museum possesses three examples of this ; we find others men- 

 tioned in different works *. 



Some have concluded from this, that the course traversed by the 

 balls must have been filled up by the very juices of the tusk and by 

 its organizing strength f ; or, as Haller says, by a species of stalactite | ; 

 but it is easy to see, on the contrary, that there had not been any hole, 

 and that the ball had not entered at tlie side where it adheres. All 

 the portion of ivory outside the ball is similar to the rest ; it is only 

 that which immediately surrounds it that is irregular : the reason is, 

 that having come at the opposite side, it traversed the alveolus, and 

 the still thin base of the tusk of a young elephant, and lodged in the 

 pulpy nucleus, which was still in all its developement ; it was then 

 held by the layers transuded by this nucleus, and remained there. 



Camper gave this explanation of it already (Descript. Anat. d'un 

 Elephant, p. 54). 



We can deduce no consequence from this fact, calculated to establish 

 the nutrition of ivory by intus-susception. 



For the same reason, it proved nothing against the opinio :: of Du- 

 hamel regarding the formation of bones by the hardening of the suc- 

 cessive layers of periosteum, though Haller thence derived one of his 

 principal arguments. 



With respect to the diseases of ivory, those which regard the alter- 

 ation of its tissue come obviously from a disease in the pulpy nucleus, 

 at the time it secreted the altered portion; and what is called exostosis 

 is always within, and never outside. It is the effect of a secretion 

 momentarily too abundant in a certain point. 



Besides, portions of the canine teeth of the morse (trichecus rosma- 



* Blumenbacli Manual d'Anat. Comp. Gallaudat, Mem, de I'Ac. de Haarlem, ix, 

 352; Bonn, Thes. Hovian., p. 146 ; Camper, An. d'un. El. pi. xx. fig. xiand xii, ; 

 Haller, Op, min., 11, p. 554. 



t Haller, Phy?., viii, p. 319. , 



X lb., p. 330. 



