DEVELOPMENT. 305 



from the capsule covering the coronal part of the dentinal pulp. In 

 the simple teeth the secondary or enamel-pulp covers the crown like a 

 cap ; in the complex teeth it sends processes into depressions of the 

 crown, which vary in depth, breadth, direction, and number, in the nu- 

 merous groups of the Herbivorous and Omnivorous quadrupeds. The 

 dentinal pulp, thus penetrated, offers corresponding complications 

 of form ; and, as the capsule follows the enamel-pulp in all its folds 

 and processes, the external cavities or interspaces of the dentine 

 become occupied by enamel and cement ; the cement, like the capsule 

 which formed it, being the outermost substance, or having the 

 enamel interposed between it and the dentine. The dental matrix 

 presents the most extensive interdigitation of the dentinal and enamel 

 pulps in the Capybara and Elephant. The processes of formation 

 and calcification of the several constituents of Mammalian teeth 

 have been already described in the Introduction (1). 



The matrix of the Mammalian tooth sinks into a furrow and 

 soon becomes inclosed in a cell in the substance of the jaw-bone 

 from which the crown of the growing tooth extricates itself by 

 exciting the absorbent-process, whilst the cell is deepened by the 

 same process and by the growth of the jaw, into an alveolus for 

 the root of the tooth. When the formative parts of the tooth are 

 reproduced indefinitely to repair by their progressive calcification 

 the waste to which the working surface of the crown of the tooth 

 has been subject, the alveolus is of unusual depth, and of the 

 same form and diameter throughout, except in the immature ani- 

 mal when it widens to its base. In teeth of limited growth, the 

 dentinal pulp is reproduced in progressively decreasing quantity 

 after the completion of the exterior wall of the crown, and forms 

 by its calcification one or more roots or fangs, which taper more 

 or less rapidly to their free extremity. The alveolus is closely 

 moulded upon the implanted part of the tooth ; and it is worthy 

 of special remark that the complicated form of socket which results 

 from the development of two or more fangs is peculiar to animals 

 of the class Mammalia(2). 



(1) P. xli. 



(2) On the strength of this generaUzation I have established the Mammahan nature of the 



X 



