28 



.I01IAN KM R. 



[SEC. ARCT. EXP. FHA.M 



HI the skeleton mass. The pulp cavities are generally narrow, canal- 

 likf. ami arc in connection with the underlying vascular canals hy means 

 ..I a narrow opening of the nature of a canal. The denticles are coin- 

 pi'M-d, as usual, of fine dentine tubules: in the spaces between the 

 denticles \\ e also find intermediary lumdles of dentine tubules, that 

 emerge from the underlying canal system and rise amongst the surface 

 denticles. This peculiarity is especially characteristic. In the peripheral 



Ski-lfli >li<>\\ iiif,' tin- stnirluri' of tlir ili-rinal skeleton of Px(unni(>steus c<ni>li<-<i- 

 -ji. Tin- iliTinal ski'ldon is nit tlimugli in several directions. At the top we 



srr tlir il.'iiticlo willi llieir pul|> i-avities and line ilcnlim- tnlniU's; liolwecn them 

 \\i>- iiili-nnciliary Ininilli'^ of dentine liilnilf- anil under. Ilir \a>cular canal system. 



part of the frag nt the vascular canals are narrow with thick walls: 



laither inwards they become wider, hut there too the walls are thick 

 with strongly marked dark median layer and lamellar structure. In the 

 longitudinal section we see straight canals, which are sometimes more 

 irregular, and extend in lacuna! fashion, often entering into connection 

 with each other hy means of large or small orifices and line canals. 



The fragmenl described in I. shows a similar microscopic structure : 

 the \a-cnlar canal -yslem. however, is wider in this case, and in the ln\\er 

 part of the plate the latter has thinner walls. 



