202 



ANIMAL PHYSIOLOGY. 



[LESSON 5V. 



859. But the extent of the ramified tubuli must be sought for in 

 a transverse section, a figure of which is given (Fig. 328) ; in the 

 centre is seen the section of the vascular canals, and the tubuli coming 

 off in profuse plexuses ; the tissue which separates the vascular 

 canals and dentinal tubuli, is a thin layer of cementum. 



860. A fossil Shark's tooth (Fig. 329) shows the structure of 

 osteo-dentiue very satisfactorily, and, to add to the beauty of the 



FIG. 323. 



FIG. 829. 



Transverse section of tooth of Myliobatis. Longitudinal section of tooth of Shark, Fossil- 



preparation, as seen by the microscope, the blood contained in the 



canals retaining its original color, is also fossilized ! 



861. Here the canals (a) are seen to be wavy, and anastomosing 



very freely ; the chief distribution of the dentinal tubuli is to the 



sides and crown (b), as in the Pristis and Myliobatis. 



Another fine example of osteo-dentine is met with in the teeth of 

 FIG. 330 the Maskanonge, call- 



ed generally Husca- 

 longe. It is a trans- 

 verse section (Fig. 

 330), and shows the 

 amastomosing charac- 

 ter of the vascular ca- 

 nals very satisfactorily. 

 Near the outer margin 

 of the tooth a canal 



Transverse section of tooth, Muscalomre. appears to run round 



it, from whence the great distribution of osteo-dentine comes off. 

 In the central portion of the section these tubuli are seen anasto- 



