. The development of the human body : a manual of human embryology. Embryology; Embryo, Non-Mammalian. 170 DEVELOPMENT OF THE SKULL anatomy that the human skull is composed of a primitive unseg- mental chondrocranium plus four vertebrae, the latter being added to and incorporated with the occip- ital portion of the chondrocranium. Emphasis must be laid upon the fact that the cartilaginous por- tion of the skull forms only the base and lower portions of the sides of the cranium, its entire roof, as well as the face region, showing no indication of cartilage, the mesen- chyme in these regions be
. The development of the human body : a manual of human embryology. Embryology; Embryo, Non-Mammalian. 170 DEVELOPMENT OF THE SKULL anatomy that the human skull is composed of a primitive unseg- mental chondrocranium plus four vertebrae, the latter being added to and incorporated with the occip- ital portion of the chondrocranium. Emphasis must be laid upon the fact that the cartilaginous por- tion of the skull forms only the base and lower portions of the sides of the cranium, its entire roof, as well as the face region, showing no indication of cartilage, the mesen- chyme in these regions being con- verted into fibrous connective tissue, which, especially in the cranial re- gion, assumes the form of a dense membrane. But in addition to the chondro- cranium and the vertebras incorpo- rated with it, other cartilaginous ele- ments enter into the composition of the skull. The mesenchyme which occupies the axis of each branchial arch undergoes more or less com- plete chondrification, cartilaginous bars being so formed, certain of which enter into very close rela- tions with the skull. It has been seen (p. 92) that each half of the first arch gives rise to a maxillary process which grows forward and ventrally to form the anterior boundary of the mouth, while the remaining portion of the arch forms the mandibular process. The whole of the axis of the mandib-. J-^V:y: Fig. 104.—Frontal Section through the occipital and upper Cervical Regions of a Calf Embryo of MM. ai and ai1, Intervertebral arteries; be1, first cervical intervertebral plate; bo, suboccipital intervertebral plate; c1— 2, cervical nerves; eh, notochord; K, vertebral centrum; ml—3, occipital myotomes; m4—5, cervical myotomes; 01—3, roots of hypoglossal nerve; vj, jugular vein; x and xi, vagus and spinal accessory nerves.—(Froriep.). Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these i
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