228 ON THE DEVELOPMENT OF THE TEETH 



Sharpey.i Not unfrequently the basement membrane of the capsule 

 is quite naked, but I have sometimes observed a Hning of short 

 cylindrical nucleated epithelium cells upon' it. 



I have said that a whitish substance lies between the basement 

 membrane of the pulp and that of the capsule. It is delicate and 

 friable, but frequently forms a more resisting layer towards the pulp. 

 On this surface I have found it to be composed of a layer of elongated, 

 more or less cylindrical epithelium cells i-ioooth of an inch in length,, 

 with or without nuclei, and adhering together in the direction of their 

 short diameters. On the surface towards the capsule, on the other 

 hand, this substance is composed of irregular cells united into a 

 network {fig. 7), and very similar to those which have been described 

 in the Skate. The structure of this substance, and its relation to the 

 basement membrane of the pulp, and of the capsule, clearly indicate 

 that it is nothing more than the altered epithelium of these organs.^ 

 It is the so-called ^'enamel-organ" of authors, and very wonderful 

 figures and descriptions indeed have been given of it in various works 

 upon the teeth. The only detailed,-' and at the same time, as it seems 

 to me, completely accurate account I have met with of this so-called 

 enamel organ, is the very clear and admirable description by Mr 

 Nasmyth, contained in his posthumous work, ' Researches on the Devel- 

 opment, Structure, and Diseases of tlie Teeth', 1849. The merits of 

 this gentleman have met with such scant justice that I cannot do 

 better than let them speak for themselves in this place ; those who 

 work over the subject hereafter will not fail, I think, to acknowledge 

 them as I have done. 



Development of the Formative Organs of the Teeth, Follicular stage. — 

 " At an early period of the follicular stage when the apex of the 



^ See also Goodsir, /. i. p. 17. In a child at birth " the interior of the sac had a villous, 

 highly vascular appearance, like a portion of injected intestinal mucous membrane.' See 

 also p. 25 of the same admirable essay. 



' Goodsir (' Edin. Med. and Phys. Journal,' 1839) and Todd and Bowman (' Physiological 

 Anatomy') state very distinctly that the pulp is an ordinary papilla, and the capsule an 

 involution of the mucous membrane, and the latter justly described the merabrana pre- 

 formativa of the pulp as a basement membrane (p. 175), but they consider the "stellate 

 tissue " and the enamel organ to be the " wall of the sac itself." Kolliker (' Mikr. Anat. ,' 

 p. loi) expresses the same opinion. 



^ Mr. Tomes (' Lectures,' &c. , 1848) appears to me to have described the enamel organ 

 very accurately, but he has, I think, failed to distinguish the proper enamel organ or 

 epithelium of the sac from the submucous cellular tissue — the latter is his " reticular stage 

 of the enamel pulp," the former his " second stage " or " stellate tissue," while what he calls 

 the "transition part,'' p. 99, is, I think, the dense superficial layer of the capsule, very 

 well described by Mr. Nasmyth (vide infra) as " the internal lamina of the dental capsule." 



Professor Kolliker ( ' Mikr. Anat. ,' p. 99 B) appears to me to have fallen into the same 

 errr)r. 



