Fetal vertebrae develop through endochondral ossification from a preexisting model. the second step of repair of a fracture of these bones is the formation of a(n) callus.

1. hyaline cartilage

2. a fibrocartilage

Explanation:

In endochondral ossification to produce fetal vertebrae, cartilage is substituted with a bone. The process of endochondral ossification includes the development of hyaline cartilage, also called the cartilage model. The hyaline cartilage develops from the chondroblasts derived from mesenchymal cells. The division of chondroblasts results in the growth of hyaline cartilage. It is followed by the development of the primary ossification center wherein the cartilage tissue is replaced with the bone matrix.  

During the repair of these bones, a fibrocartilage callus is formed. Fibroblasts present in the site where the bone is broken produce collagen fibers and the cells derived from periosteum develop into chondroblasts and begin to produce fibrocartilage in this region. The fibrocartilage and collagen fibers together make the fibrocartilage callus that joins the broken ends of the bone.

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