lume, "that
the idea of a natural segment (vertebra) of the endoskeleton does not
necessarily involve the presence of a particular number of pieces, or
even a determinate and unchangeable arrangement of them. The great
object of my present labour has been to deduce ... the relative value
and constancy of the different vertebral elements, and to trace the kind
and extent of their variations within the limits of a plain and obvious
maintenance of a typical character" (p. 146).

It goes without saying that Owen considered the skull to be formed of
vertebrae--the vertebral theory of the skull was, in his system, a
deduction from the vertebral theory of the skeleton. He recognised four
cranial vertebrae; the arrangement of them, and the relation of their
constituent bones to the parts of the typical vertebra are shown in the
table appearing on page 106. So far as their first three elements are
concerned, these vertebrae are practically identical with the vertebrae
distinguished in the classical vertebral theory of the skull, as
enunciated by Oken. A divergence appears with the determination of the
other elements of the vertebrae. The upper and lower jaws are associated
with the nasal and frontal vertebrae respectively, not however as limbs
of the head, but as constituent elements of these vertebrae. In the same
way the hyoid apparatus is part and parcel of the parietal vertebra, and
the pectoral girdle and fore-limbs part of the occipital vertebra.

[Illustration: FIG. 6.--The Archetype of the Vertebrate Skeleton. (After
Owen.)]

Cranial Vertebrae.[164] (After Owen, 1848, p. 165.)

+---------------+---------------+----------------+---------------+-------------+
| Vertebrae. | Occipital. | Parietal. | Frontal. | Nasal. |
+===============+===============+================+===============+=============+
|Centra. |Basioccipital. |Basisphenoid. |Presphenoid. |Vomer. |
+---------------+---------------+----------------+---------------+-------------+
|Neurapophyses. |Exoccipital. |Alisphenoid. |Orbitosphenoid.|Prefrontal. |
+---------------+---------------+----------------+---------------+-------------+
|Neural Spines. |Supraoccipital.|Parietal. |Frontal. |Nasal. |
+---------------+---------------+----------------+---------------+-------------+
|Parapophyses. |Paroccipital. |Mastoid. |Postfrontal. |None. |
+---------------+---------------+-------------