SCAROIDS. 113 



excavation or concavity, in the middle of wliicli there is a small oval 

 articular depression, to which a corresponding convex trochlea of 

 the maxillary bone is adapted. Powerful muscles are inserted into 

 the two produced angles of the intermaxillary bone, by means of which 

 it is worked upon the hinge-like joint above described. The 

 premandibular piece of the lower jaw differs from the intermaxillary 

 bone above in the absence of the posterior median process, but 

 in other respects it closely resembles that bone in form. 



When the intermaxillary and premandibular bones are viewed 

 from their outer side, they appear to be edentulous, and to have 

 their osseous texture converted, at the anterior and outer part, 

 into an enamel-like substance, with a surface chequered by small 

 lozenge-shaped smooth or tuberculate plates arranged in a quin- 

 cuncial order, (PL 49, fig. 1). When viewed from the inside, (PL 49, 

 fig. 3), the irregular trenchant margin of these bones is seen to be 

 composed of short and thick sub-conical four-sided columns, placed 

 almost vertically to the outer surface of the jaw, along a great part 

 of which surface similar columns are arranged, which form by their 

 exposed bases the tesselated surface above mentioned. These small 

 columns are the teeth ; the exposed base is the crown, and the oppo- 

 site contracted end, which is slightly excavated, corresponds with the 

 fang(l). If a vertical section of the jaw be made, as in fig. 3, these teeth 

 or denticles will be exposed in various stages of formation in a cavity 

 (6) below the dental series in the premandibulars, and in the reverse 

 situation in the intermaxillaries. The formative quadrilateral pulps 

 are contained in this cavity, with their bases attached to the vascular 

 membrane lining its posterior wall, and with their free extremities pro- 

 jecting horizontally forwards towards the anterior or outer wall. 

 Alveolar or capsular processes of vascular membrane are continued 

 backwards from the outer wall and inclose the pulps, like the 

 capsule of the matrix of ordinary teeth. At the uppermost part of 

 the dentigerous cavity in the upper jaw, the broad anterior extremity 

 of the columnar tooth is seen to be formed by calcification of the 

 summit of the pulp : a little lower down, the whole length of the 

 tooth is completed, but the ba-se is excavated by a conical 



(1) Cuvier, Lemons d'Anatoraie Comparee, Nouv. Ed. Paris, 1836, torn, iv, p. 226. 



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