Mechanism of the reduction of Meckel's cartilage in man

The mechanism of reduction of the anterior end of Meckel's cartilage was studied in human embryos, with the following findings: 1. Meckel's cartilage is surrounded, from the outside and from below, by newly formed mandibular bone over the extent of the insertion of the musculus mylohyoideus. 2. Blood vessels from the newly formed bone penetrate Meckel's cartilage and break it down in the same way as in enchondral ossification of cartilaginous models of other bones. 3. The anlagen of the musculus mylohyoideus and musculus genioglossus are at first inserted on Meckel's cartilage; further muscle fibres, formed on the under surface of the two muscles, are inserted on the newly formed bone of the rudimentary mandible. Parallel to this process, the fibres on the upper surface of the muscles, which were originally inserted on Meckel's cartilage, disappear. The two processes combined lead to transposition of the insertions of the two muscles from Meckel's cartilage to the mandible. 4. In the area of the resorbed Meckel's cartilage, a minimum number of bone trabeculae are formed at the time of its resorption. The space left by Meckel's cartilage is taken over chiefly by the primitive medullary cavity of the rudimentary mandible, medially to the canal for the nerve and blood vessels.