MAMMALIA. 665 



its pulp ; so that each plate is necessarily hollow at its growing 

 end, the first part of the growth taking place on the inside of this 

 hollow." 



" Besides this mode of growth, which is common to all such 

 substances, it receives additional layers on the outside, formed 

 from the above-mentioned vascular substance, extended along the 

 surface of the jaw. This part also forms upon it a semi-horny 

 substance between each plate, which is very white, rises with the 

 whalebone, and becomes even with the outer edge of the jaw. This 

 intermediate substance fills up the spaces between the plates as 

 high as the jaw ; acts as abutments to the whalebone; or is similar 

 to the alveolar processes of the teeth, keeping them firm in their 

 places. 1 ' 



"As both the whalebone and intermediate substance are con- 

 stantly growing, and as we must suppose a determined length ne- 

 cessary, a regular mode of decay must be established, not depend- 

 ing entirely on chance, or the use it is put to. In its growth, 

 three parts appear to be formed : one from the rising cone, which 

 is the centre ; a second on the outside ; and a third, being the in- 

 termediate substance. These appear to have three stages of dura- 

 tion ; for that which forms on the cone, I believe, makes the hair, 

 and that on the outside makes principally the plate of whalebone : 

 this, when got a certain length, breaks off, leaving the hair project- 

 ing, becoming at the termination very brittle : and the third, or 

 intermediate* substance, by the time it rises as high as the edge of 

 the skin of the jaw, decays and softens away like the old cuticle of 

 the sole of the foot when steeped in water." 



(745.) Other kinds of teeth, met with among Mammals, are com- 

 posed of calcareous earths deposited in a nidus of animal matter, and 

 consequently resemble bones in 

 the hardness of their texture. In F 'g- 31 * 



their simplest form these teeth 

 consist of but one kind of mate- 

 rial, called ivory; and in such 

 cases there' is no distinction into 

 classes as in the human sub- 

 ject, every tooth being conical, 

 and formed upon a simple pulp. 

 Such are the teeth of the Por- 



* Mr. FTunter means, by " intermediate," interposed between the contiguous plates, 

 not between the " hair" and the laminated whalebone. 



