Sections of the matrix of developing dentin and enamel from the foetal pig, alligator lizard, bullfrog and trigger-fish were examined with scanning electron microscopy. The major difference appears to be in the number and size of the tubules that permeate the matrices. The pre-dentin matrix is a loose meshwork of fibrillae surrounding the area of the dentinal tubules. The older circumpulpal dentin intertubular matrix is fibrillar, with the interstices of the matrix filled with an amorphous ground substance. The enamel organic matrix has a fibrillar appearance, with no evidence of rod structure being seen.
Observed for the first time is an apparent system of microtubiculi with diameters of about 0.2µ permeating the enamel matrix. Such a system of microtubiculi would provide a pathway for diffusion of inorganic salts and for the removal of soluble organic material during amelogenesis. The similarity of development and structure in amphibians and reptiles suggests the possibility of utilizing these animals in experimental mineralization studies.