Development of the pars membranacea septi interventricularis of the human heart. I. Collagen fibers, fixed connective cells and amorphous fundamental substance.

Abstract

The development of the pars membranacea septi interventricularis of the human heart, from the closure of the secondary interventricular foramen to the end of the fetal age, presents two phases well separated by a period of transition between the 119 mm long (CR) fetus, corresponding to 15.1 weeks, and the 149 mm long (CR) fetus, corresponding to 17.1 weeks. In the I phase, 78% the fixed connective cells and 22% of the amorphous fundamental substance were replaced by bundles of collagen fibers. In the II phase, 75% of the amorphous fundamental substance and 25% of the fixed connective cells were replaced by bundles of collagen fibers.