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I. The chondrocranium, jaws, arches, and muscles of a partly grown larva.

The deficiencies in the chondrocranium appear in the occipital bone, which requires a small portion of the dermal bone to complete it on each side.

Owing to the struggle for existence which occurs at puberty between the old type of the chondrocranium and its new type as supplemented by the dermal bones, the nervous system takes a distorted ply which arrests both the bodily, nervous, and mental development at certain points.

Behind, the primary skull or chondrocranium gives off two occipal or rear skull plates.

The fontanelles, or soft places at the top, sides, and back of the head of the new-born child, are the remains of this failure of the chondrocranium, or primary skull, to cover the gains of the nervous system in the struggle for existence.