The function of Meckel's and secondary cartilages in the histomorphogenesis of the cat mandibular symphysis.

Cat mandibular symphysis was investigated with histological methods in animals of ages between 3 weeks of intra-uterine life and 56 days post-natal. As in rodents, carnivores and insectivores, Meckel's cartilages fuse in the midline and form a cartilaginous nodule which persists in the symphysis until birth. This nodule, which we have called the symphyseal Meckelian islet, is isolated from Meckel's cartilage, of which only very small calcified islets are left as intramandibular traces after endochondral ossification. Both hemimandibles are bordered by secondary cartilage, which undergoes endochondral ossification, and by chondroid tissue, which is less abundant than in man. At birth, secondary cartilage of both hemimandibles forms a synchondrosis, the lingual part of which undergoes gradual resorption in the 4-week-old cat. The vestibular part is still present at 8 weeks.