110 LABROIDS. 



pulp-cavity. This is gradually diminished by a formation of dentine 

 from the margins of the base, which encroaches towards the centre, 

 until it finally forms a partition between the pulp-cavity and the 

 alveolus. 



In most of the specimens of the pharyngeal bones of the Wrasse- 

 tribe, some of the alveoli are empty, and the round extremity of a 

 new tooth is generally seen protruding for a greater or less extent 

 through the cribriform base. When a vertical section of one of these 

 paved pharyngeals is made, as in Plate 46, figure 1, a regularly formed 

 cavity is exposed beneath the base of each of the bisected teeth, 

 containing a successional tooth (&), more or less advanced in growth. 

 Smaller cavities for lodging processes of the formative pulp are seen 

 extending from the base of those containing the most advanced teeth, 

 and forming the rudiments of future alveoli. 



When the structure of one of these pharyngeal molars is micro- 

 scopically examined, in a thin vertical section, numerous densely 

 aggregated and extremely fine calcigerous tubes are observed to 

 radiate in all directions from the pulp-cavity, and in a direction ver- 

 tical to the plane of the surface from which they are continued. 

 Those which descend, soon terminate in cells that communicate with 

 the canals in the thin plate of bone to which the tooth is affixed. 

 Those which pass out laterally towards the side of the tooth, follow 

 the curve of the side as it rises from the base, and form a band with 

 the convexity next the base. Those which pass to the upper surface 

 and upper part of the lateral surface, have a pretty direct course : 

 but all the tubes, when viewed with a high power, are found to be 

 minutely and beautifully undulated. 



When they reach the clear enamel-like covering of the tooth, 

 the calcigerous tubes lose their undulatory disposition, and instead of 

 continuing parallel, they cross each other in graceful curves in all di- 

 rections. 



In the small scale on which such a section as has been described 

 is figured (PL 46), only the general course of the calcigerous tubes 

 can be indicated ; but it is impossible to view the disposition of these 

 minute hollow columns, in connection with the mode in which the 

 whole tooth is fixed in its alveolus, without being forcibly struck 



