THE DIGESTIVE SYSTEM 



233 



,v 



the root it communicates with the underlying tissue by means of one 

 or more minute apical foramina, through which blood-vessels and 

 nerves enter the pulp ca\'ity. 



The dental pulp consists of loose connective tissue approaching the 

 embryonal in type, composed of many fusiform and stellate cells 

 and dcHcate white fibrils which do 

 not form bundles but interlace in all 

 directions. There arc apparently 

 no elastic fibres. A few smooth 

 muscle cells have been described. 

 The pulp is richly supplied with 

 blood-vessels and nerves which are 

 found only in this part of the tooth. 

 Along the dentinal surface of the pulp 

 the connective- tissue cells are ar- 

 ranged as a single layer of columnar 

 cells, the odontoblasts. These cells 

 are about 40yu long and lie with 

 their long axes at right angles to the 

 surface. They are closely allied to 

 osteoblasts. Their nuclei lie toward 

 their inner ends. Each cell sends 

 out an inner process, which is usually 

 single and passes into the dental pulp, 

 several lateral processes which inter- 

 lace with and probably anastomose 

 with similar processes from other 

 cells, and one or more outer fibre- 

 like processes which enter the den- 

 tine, where they form the dentinal 

 fibres. These frequently extend en- 

 tirely through the dentine. Just 

 beneath the layer of odontoblasts, the connective-tissue cells are 

 much fewer in number than in the rest of the dental pulp. Appear- 

 ing in sections as a clear band, it is known as the layer of Weil. 

 Immediately internal to the layer of Weil, the cells are more closely 

 arranged than elsewhere in the pulp. 



Dentine (Figs. 139 and 140, D) is somewhat harder than bone 

 which it resembles in structure. According to von Bibra its chemical 

 composition is: 



Fig. 137. — Vertical Section of 

 Tooth, in situ. X15. (Waldeyer.) 

 c, Pulp cavity, the letter being at 

 about the junction of crown and 

 root; I, enamel showing radial and 

 longitudinal markings; 2, dentine 

 showing dental canals; 3, cementum 

 (containing' bone corpuscles); 4, peri- 

 dental membrane; 5, bone of lower 

 jaw. 



