TILE MORPHOLOGY OF THE SKULL is the highest and most difficult problem of comparative anat omy. Huxley destroyed the archetypal theory, previously held by Owen and others, and estab lished the newer theory on sure grounds of actual observation. Taking first the unsegmented cra nium of a skate or dogfish, with its appended jaws and arches, we find that in development, though the notochord extends into the region of the head, the vertebrae stop short of it; but that on each side of the cranium there arise a pair of cartilaginous bars, the trabcculcc or rafters of the future skull; three pairs of cartilaginous cap sules, nasal, ocular, and auditory, form round the developing sense organs; the nasal cap sules unite with the ends of the trabecula-, which are meanwhile uniting below, and growing up at the sides to form the brain-case. The auditory capsules become united with the trabecuhe by the appearance of two new masses of cartilage, the parachordals. The first pair of a series of
seven or more arches develops an ascending pro cess, becoming the palato-pterygoid arch or upper jaw. The necond pair of arches, the hyoid, is modified to support the jaws, while the rest are modified to support the gills. In the bony skulls of higher vertebrates the chondro-cranium and subjacent arches develop in the same way. The bones originate in two distinct ways: either by actual ossifications o• by the ossification of over lying, dermis, known as cartilage bones and mem brane bones respectively, the latter corresponding to the dermal bones and teeth of ganoid and elas mobranch fishes. In mammals the ends of the mandibular and hyoid arches lose their suspen sory function, are taken into the interior of the ear capsule, and are metamorphosed into the auditory ossicles. See SKELETON.