484 SPECIAL HISTOLOGY. 



by shorter and rounder cells, without any sharp lines of demarcation, 

 into the vascular tissue of the pulp. These cells corespond with the 

 formative cells of the dentine, to be described presently, and they afford 

 the materials for the deposits of dentine upon the walls of the pulp 

 cavity, which takes place even in the adult. 



The vessels of the pulp are excessively numerous, whence its red color. 

 3-10 small arteries enter each pulp of a simple tooth, and ultimately 

 form, as well in its interior as upon its surface, a loose plexus of capil- 

 laries, 0-004-0-006 of a line in diameter, which also exhibits here and 

 there upon the surface distinct loops from which the veins arise. The 

 pulp appears to contain no lymphatics, but its nerves* are extremely 

 abundant. Arising from the well-known nervi dentales, there passes 

 into every fang a large trunk of 0-03-0-04, and besides, as many as six 

 or more, fine branches of 0-01-0-02 of a line, which contain fibres of 

 0-0016-0-003 of a line. They ascend at first without any considerable 

 anastomoses and only giving off a few filaments ; but in the thicker part 

 of the pulp they form a rich plexus, with elongated meshes and divisions 

 of the nerve tubules, and so gradually break up into fine primitive 

 fibres of 0-001-0-0016 of a line. I am inclined to think their final 

 termination is in loops, but I grant that so long as the primitive fibrils 

 in those loops which unquestionably do occur, have not been traced from 

 trunk to trunk, which no one has yet done, the subject is open to doubt. 



The gum, yingiva, that portion of the oral mucous membrane which 

 unites the alveolar margins of the jaw and the necks of the teeth, is a 

 pale red vascular tissue, which is tolerably soft, but feels firm on ac- 

 count of the subjacent hard parts : it, attains, where it lies upon the 

 teeth, a thickness of J-l J lines, and possesses papillae of a considerable 

 size (of 0-15-0-3 of a line; in old people they even reach 0-7 of a line 

 in length, and like the papillce filiformes are covered with secondary 

 papillae), and a pavement epithelium, which, between the papillae, has a 

 thickness of 0-23-0-4 of a line. I could find no glands upon the gum, 

 but care must be taken not to confound with them certain rounded de- 

 pressions of the epithelium of 0'8-0-15 of a line in diameter, with 

 more cornified cells, which occur not unfrequently upon its upper por- 

 tions. 



142. Development of the Teeth. The development of the twenty 

 milk teeth commences in the sixth week of foetal life, by the formation 

 of a groove in the upper and lower margin of the jaws, in which, 

 up till the tenth week, twenty dental papillae gradually make their ap- 



* [The nerves of the alveolar periosteum and of the pulp, are particularly described by 

 Czermak (1. c. pp. 27, 28). TBS.] 



