. The development of the human body : a manual of human embryology. Embryology; Embryo, Non-Mammalian. OSSIFICATION OF BRANCHIAL ARCH SKELETON 179. Fig. i 10.—Diagram of the Ossi- fications of which the Maxilla is Composed, as seen from the Outer Surface. The Arrow Passes through the Infraor- bital Canal.—{From von Spee, after Sappey.) the palatine and maxilla, are developed in it, their cartilaginous representatives, which are to be found in lower vertebrates, having been suppressed by a condensation of the development. The palatine bone develops from a single center of ossification, but for
. The development of the human body : a manual of human embryology. Embryology; Embryo, Non-Mammalian. OSSIFICATION OF BRANCHIAL ARCH SKELETON 179. Fig. i 10.—Diagram of the Ossi- fications of which the Maxilla is Composed, as seen from the Outer Surface. The Arrow Passes through the Infraor- bital Canal.—{From von Spee, after Sappey.) the palatine and maxilla, are developed in it, their cartilaginous representatives, which are to be found in lower vertebrates, having been suppressed by a condensation of the development. The palatine bone develops from a single center of ossification, but for each maxilla no less than five centers have been described (Fig. no). One of these gives rise to so much of the alveolar border of the bone as contains the bicuspid and molar teeth; a second forms the nasal process and the part of the alveolar border which contains the canine tooth; a third the portion which con- tains the incisor teeth; while the fourth and fifth centers lie above the first and give rise to the inner and outer portions of the orbital plate and the body of the bone. The first, second, fourth, and fifth por- tions early unite together, but the third center, which really lies in the ventral part of the nasal process, remains separate for some time, forming what is termed the premaxilla, a bone which remains per- manently distinct in the majority of the lower mammals. The above is the generally accepted view as to the development of the maxilla. Mall, however, maintains^ that it has but twro centers of ossification, one giving rise to the premaxilla and the other to the rest of the bone. The maxillary center makes its appearance about the middle of the sixth week. Since the condition known as hare-lip results from a failure of the maxillary process to unite completely with the frontonasal process (see p. 100), and since the premaxilla develops in the latter and the maxilla in the former, the cleft may pass between these two bones and prevent their union (see a
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