. The chordates. Chordata. 112 Basic Structure of Vertebrates BASIS PHENOID ORBITOSPHENOID \ ALISPHENOID PRESPHENOID \ \ \ PARIETAL FRONTAL VOMER PREFRONTAL NASAL SUPRAOCCIPITAL EXOCCIPITAL , BASIOCCIPITAL. MAMMAL Fig. 110. One of Owen's figures illustrating the Goethe-Oken vertebral theory of the skull. Owen regarded the mammalian skull as constituted of four enlarged and highly modified vertebrae (their centra shown in solid black). (After Wilder. Courtesy, Neal and Rand: "Chordate Anatomy," Philadelphia, The Blakiston Company.) into the more complex brain. Similarly, the axial ske
. The chordates. Chordata. 112 Basic Structure of Vertebrates BASIS PHENOID ORBITOSPHENOID \ ALISPHENOID PRESPHENOID \ \ \ PARIETAL FRONTAL VOMER PREFRONTAL NASAL SUPRAOCCIPITAL EXOCCIPITAL , BASIOCCIPITAL. MAMMAL Fig. 110. One of Owen's figures illustrating the Goethe-Oken vertebral theory of the skull. Owen regarded the mammalian skull as constituted of four enlarged and highly modified vertebrae (their centra shown in solid black). (After Wilder. Courtesy, Neal and Rand: "Chordate Anatomy," Philadelphia, The Blakiston Company.) into the more complex brain. Similarly, the axial skeleton continues forward and becomes elaborated into a suitable protective structure, not only for the brain but also for the three pairs of important sense organs of the head, the nasal organs, eyes, and ears. This anterior terminus of the axial skeleton is the cranium, a part of the skeletal complex known as the "; In the structure of the cranium are features which suggested to the early anatomists that it is virtually a series of expanded and modified vertebrae. Thus the atlas articulates with the ventral portion of a complete ring constituted of four bones. A massive midventral boue, the basioccipital, underlies the rear part of the brain. At each side the basioccipital joins an exoccipital and the ring is completed dorsally by the supraoccipital (Fig. 110). This whole occipital arch of four bones can be imagined to be a vertebra, its centrum being the basioccipital surmounted by a "neural arch'' enclosing the central nervous organ. The arrangement of cranial bones anterior to the occipital ring is such as to suggest a series of two or three more modified vertebrae. The vertebral column is concerned pri- marily with muscular action, but incidentally affords protection to the overlying central nervous organ. The cranium serves mainly as protec- tion for the brain and is to a relatively small extent concerned with muscles. Leaving aside questions of interp
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