CAETILAGE. BONE. TEETH. 41 



placed side by side, without any appreciable inter- 

 vening substance (PL VIII. fig. IV. 1). Examined 

 in vertical section they are observed to undulate 

 slightly, and to assume a direction perpendicular to 

 the nearest surface ; moreover, they are generally 

 parallel with each other, except upon the irregularly 

 shaped surfaces of the molar teeth, where they form 

 divergent bundles (PL VIII. fig. III.). Their sub- 

 stance is wholly amorphous ; sometimes it is crossed 

 by transverse lines ; its chemical nature seems to 

 connect it with the epithelial formations. Some 

 observers have asserted that the enamel is invested 

 externally by a delicate structureless layer, which 

 they designate as the cuticle of the enamel. 



The cementum, by which the root of the tooth is 

 covered externally, is true bone ; it consists of funda- 

 mental substance, and bone-cells of variable size and 

 irregular in their arrangement. Haversian canals are 

 absent, except where its structure has been altered 

 by inflammation. The periosteal investment of the 

 alveolar sockets also covers the surface of the ce- 

 mentum. 



The pulp of the tooth, which occupies its central r>entai p ui p . 

 cavity, is connected with the periosteum of the socket 

 by a pedicle which penetrates the orifice at the 

 pointed extremity of its root. It is made up of deli- 

 cate connective tissue, interspersed with plasmatic 

 cells, and largely supplied by blood-vessels and 

 nerves the terminal arrangement of the latter being, 

 as yet, imperfectly made out. The presence of lym-^ 

 phatic vessels in the pulp is uncertain. During the Development of 

 sixth week of foetal life, the free borders of the niax- 



3 



