238 DENTINE OR IVORY. 



and are imbedded in the osseous substance. These fibres 

 are solid, instead of tubular as supposed by Ketzius and 

 others, and they present (from the peculiar arrangement 

 of their nuclei) a beaded or "baccated" appearance as 

 seen in Fig. 65, A. 



The fibres of the pulp are observed to be spiral in their 

 course, but less so, and rather undulating where the ivory 

 is deposited around them. The pulp is enclosed in a 

 double sac the outer one stated by Mr. Hunter to be 

 "soft, spongy, and without vessels," while the inner is 

 very' vascular and firm. Mr. Blake on the other hand 

 makes the outer to be full of vessels, as well as spongy, and 

 the inner to be destitute and delicate. The injections of 

 Mr. Fox, preparations of Mr. Bell, and observations of Pro- 

 fessor Harris, all seem to show that both membranes are 

 decidedly vascular. At an early period when this sac, 

 termed the dental capsule, is about to close its follicular 

 stage, from being a mucous membrane, presents, according 

 to Mr. Nasmyth, a "white, silvery, loose, and rugous" 

 appearance, which, under the microscope, exhibits minute 

 cells differing from those of the epithelium, while the inter- 

 nal layer of the sac, according to this same authority, pre- 

 sents layers of loose cells, of oval shape, containing nuclei 

 and some granular matter, but destitute of vessels. This 

 layer, however, he states, has beneath it a net-work of 

 vessels, "supported by a web of areolo-fibrous tissue/' 

 which readily accounts for both layers of the capsule being 

 considered vascular. 



The dental capsule is found to be connected with the 

 alveolar periosteum, and so blended with it, as to be con- 

 sidered a single membrane. Mr. Bell makes one of its 

 attachments inseparable from the gums, and the other con- 

 nected with the pulp, where the vessels and nerves enter. 



DENTINE OR IVORY. 



Dentine or Ivory, (see Fig. 61, A,) forms by far the 

 most abundant constituent of a tooth, composing the 

 whole of the body, root and neck, excepting the thin cov- 



