The Development of Enamel Structure in Mammals 



279 



prism than do those in Pattern 3 prisms. The cervical (prism body) side of the 

 depressions is concave in pig enamel (Pattern 2) but convex in elephant enamel 

 (Pattern 3). The concave shape of the cervical side would encourage parallel orien- 

 tation — the convex would encourage deviation from the mean prism axis. 



J. Sui Lii-p.iir electron micrographs of replicas (carlx'v .•; :'u' .;:itan.- nt dcx clopnv^ pii; I'liamel. Original 

 maguihcation . 5000. a) Looking down on surface fruni abo\c, loiujI to the lett. There are raised humps 

 in the middle of the cervical sides of some of the depressions (which were occupied by Tomes' processes of 

 ameloblasts); these humps are probably related to the development of "prisms within prisms", b) Looking up 

 at surface from underneath — from the enamel's point of view. The concavity of the cervical sides of the 

 depressions therefore now appears as the convexity of raised bumps 



Fig. 3. Stereo-pair electron micrograph of carbon replica of surface of developing african elephant enamel — 



looking down on surface from above. There is only one "depression" in the field of view. "Cervical" towards 



top left. This replica was released from the enamel by acid decalcification and the organic material removed 



by boiling in cone. NaOH. Adherent debris is probably mostly NaOH 



