LEPIDOGANOIDEI. 157 



Fig. 68 is one of these fossil teeth of the natural size — a, a 

 transverse section ; and fig. 69, a reduced view of a portion 

 of the same section (a) enlarged twenty diameters. Thus 

 magnified, a central pulp-cavity of 

 relatively small size, and of an ir- 

 regular lobulated form, is discerned, 

 a portion of which is shown at p ; 

 this is immediately surrounded by 

 transverse sections of large cylindri- 

 cal vascular or pulp canals of diffe- 

 rent sizes ; and beyond these there 

 are smaller and more numerous 

 medullary canals, which are pro- Fig- 68. 



cesses of the central pulp-cavity. In Tooth of D ™ d ™ dus hiporcatus 



(nat. size.) 



the transverse section these processes 



are seen to be connected together by a net-work of smaller 

 vascular canals belonging to a coarse osseous texture, into which 

 the pulp has been converted, and this structure occupies the 

 middle half of the section. All the vascular canals were filled 

 up by the opaque matrix. From the circumference of the 

 central net-work straight pulp-fissures radiate at pretty regular 

 intervals to the periphery of the tooth ; most of these fissures 

 divide once, rarely twice, in their course — the division taking 

 place sometimes at their origin, in others at different dis- 

 tances from their terminations, and the branches diverge 

 slightly as they proceed. Each of the above pulp-canals or 

 fissures is continued from a short process of the central struc- 

 ture, which is connected by a concave line with the adjoining 

 process, so that the whole periphery of the transverse section 

 of the central coarse reticulo-vascular body of the tooth pre- 

 sents a crenate outline. From each ray and its primary 

 dichotomous divisions short branches are sent off at brief 

 intervals, generally at right angles with the trunk, or slightly 

 inclined towards the periphery of the tooth. These subdivide 



