114 SCAROIDS. 



cavity containing the remains of the pulp, and the tooth is 

 loose, or is suspended only by its pulp and capsule : still lower 

 down, the capsule is observed in different stages of ossification ; 

 and the tooth becomes thereby ancbylosed, first by its anterior, and 

 afterwards by its posterior extremity, to the opposite walls of the 

 formative cavity. The ' pulp-cavity becomes diminished in size by 

 the progressive calcification of its organized contents, and at length 

 the tooth, by the complete ossification of its external capsule, 

 becomes adherent laterally to the contiguous teeth, as well as to 

 the walls af the dental cavity by its extremities : thus the dense, 

 exposed anterior portions of the premaxillary and premandibular 

 bones are converted into an aggregated and ancbylosed mass of 



teeth. 



When the microscopic structure of one of the maxillary denticles 

 is examined in a longitudinal section, the conical pulp-cavity may 

 be traced to near the coronal end of the tooth. The calcigeroas tubes, 

 which at their origin do not exceed ^^ of an inch in diameter, are very 

 closely aggregated, being separated by intervals equal to only one 

 and a half of their own diameters ; those at the base of the pulp-cavity 

 descend, and on one side of the denticle, inchne inwards, tending to 

 close that cavity ; the greater number of the calcigerous tubes proceed 

 directly outwards, at right angles to the sides of the denticle : 

 near the coronal surface they begin to bend towards that end, and 

 to pass more obliquely from the pulp-cavity, until they assume, 

 in the centre of the crown, a direction parallel to the axis of the 

 tooth. Besides the primary curvatures, which are most marked at the 

 two extremes of the denticle, all the calcigerous tubes present the 

 most regular and graceful undulations throughout their entire course : 

 these undulations require a compound lens of ^th inch focus to be 

 distinctly seen, and, with the fine lateral branches of the tubes, form 

 no mean test of the powers of the microscope employed. The pulp- 

 cavity becomes finally occupied by a coarse cellular bone, and a thin 

 coating of the same kind of tissue invests the exterior of the denticle. 

 The general disposition of the calcigerous tubes, and the form of the 

 detached denticle and its pulp-cavity are figured in PI. 50. 



The thick external enamel-hke layer of each denticle, which 



