476 STRUCTURE AND DEVELOPMENT OF TEETH, W. WALDEYER. 



regarded as nests of osteoblasts formed in the process of ossification, 

 and surrounded by thick sheaths of connective tissue. 



SOFT STRUCTURES OF THE TEETH. The soft tissues be- 

 longing to the teeth include the tooth pulp and the gums. 

 The former is the vascular and nervous matrix of the dentine, 

 and the remains of the original tooth papilla. It constitutes 

 also the model of the tooth on which the hard structures are 

 formed like a cast, and therefore presents, in accordance with 

 their difference in shape, an extremely various form. In old 

 teeth, where the hard parts predominate to a remarkable extent, 

 there remains only an inconsiderable residue of the pulp en- 

 closing the cavum dentis, and in the human tooth it is reduced 

 to a very slender thread containing a few vessels and nerves. 

 The pulp is immediately connected with the periosteum and 

 base of the alveolus by means of the foramina dentium. 



In the incisors of the Rodents, which produce new dentine con- 

 tinuously, the pulp, even in adults, retains its original character, and 

 its structure can there be best studied. 



The principal portion of a good specimen of young pulp con- 

 sists of indistinct finely fibrous connective tissue containing 

 numerous cells, that recalls in many respects the mucous tissue 

 of old atrophied umbilical cords, the elastic tissue only being 

 absent. On account of the numerous large vessels which 

 break up immediately beneath the surface into a plexus of 

 capillaries of moderate width, the tissue appears quite cavern- 

 ous. The external layer of the pulp is formed by a layer of large 

 cells, of elongated form, and provided with numerous processes, 

 called Odontoblasts (49, 59), which are arranged so as to form 

 a kind of columnar epithelium * These cells (see figs. 102, 

 103) are from 20 to 30 fi on the average in length, and about 

 5 // in breadth. They are finely granular, and destitute 

 of a membrane. The moderately large rounded or ovoid nu- 



* The names formerly applied to them were dentinal cells (Elfenbein- 

 zellen). Kolliker terms this entire layer of cells membrana eboris, because 

 after the pulp has been withdrawn it usually cleaves to the inner surface 

 of the tooth in the form of a continuous membrane-like layer. 



