134 LUCIOIDS. 



supporting process of gum is represented at Plate 44, fig. 5 ; a is 

 the superficial calcified layer of the pulp c, the base of which is sunk 

 into a fossa, or open capsule of the gum b ; d is the nerve entering 

 the base of the pulp. In figure b, PI. 44, the course of the branches 

 of the fifth pair of nerves, through the permandibular bone of the 

 pike, to supply the pulps of the teeth, is shown ; the size of the 

 dental nerve bears relation to the vascular and organized texture of 

 the tooth, and to the rapidity of its growth. 



Retzius' accurate description of the microscopic structure of the 

 tooth oHhe Vike {Esox Lucius, L.) is as follows. "It consists of an 

 internal part or nucleus with coarse tubes, and an outer thinner part, 

 with fine and parallel tubes, which form the covering of the nucleus. 

 The coarse main-tubes, which occupy the internal and imperfectly 

 developed parts of the ivory, present at their widest part a diameter of 

 about g^th of an inch. Their course is almost parallel with each 

 other and with the axis of the tooth, and they unite by numerous 

 larger or smaller anastomoses. Near the basis of the anchylosed 

 teeth, the larger oblique anastomoses are so near together that their 

 interspaces are scarce equal to the diameter of the larger tubes. In 

 recent teeth these tubes contain a blood-red substance, which might 

 be regarded as a complex pulp. Beautifully minute and very short 

 tubules of from g^ to ^th. of an inch in diameter, proceed mostly 

 in a transverse direction from the larger tubes ; and subdivide, as 

 they proceed, into groups of finer tubes, which form innumerable reti- 

 cular anastomoses with each other, and thus fill up the interspaces of 

 the larger canals. The boundary between the central and peripheral 

 substances is well defined, and is formed by anastomoses of the exte- 

 rior longitudinal bent coarse tubes ; beyond which no coarse tube 

 extends, but only a series of fine and parallel tubes ; these tubes 

 manifest the same direction as those in the thin and hollow shell of 

 the incompletely formed teeth of the higher organized animals : i. e. 

 the fine tubes that are nearest the apex of the tooth, are almost paral- 

 lel with the axis of the tooth, while those which are nearest the root, 

 proceed transversely to the axis. They soon divide into pencils of 

 finer branches, which mutually and reticularly anastomose, and give 

 off at their peripheral extremities close- set parallel tubes, from j^ to 



