d dorsal walls, proving the
essential identity of the structures involved and of their relations
to the nerve exits in the great types he had chosen. In the series of
lectures delivered before the College of Surgeons, he extended his
observations to a much larger series of vertebrates, and substantially
laid down the main lines of our knowledge of the skull. In two
important respects his statements were not merely a codification of
existing knowledge, but an important extension of it. He distinguished
the different modes in which the jaws may be suspended to the skull,
and established for these different kinds of suspensoria the names
which have ever since been employed. He proved clearly what had been
suggested by Oken, that the region of the ear is a lateral addition to
the skull, and he distinguished in it three bones, his names for which
have since become the common property of anatomists. Finally, he made
it plain beyond any possible doubt that the skulls of all vertebrates
were built upon a common plan.

Having established the facts, he proceeded to enquire into the theory.
There was now a new method for investigating such problems, the method
of embryology, which, practically, had not been available to Oken, and
of which neither Cuvier nor Owen had made proper use. By putting
together the investigations of a number of embryologists, by adding to
these himself, and, lastly, by interpreting the facts which his
investigations into comparative anatomy had brought to light, he
shewed that the vertebral theory could not be maintained. He shewed,
by these methods, that, though both skull and vertebral column are
segmented, the one and the other, after an early stage, are fashioned
on lines so different as to exclude the possibility of regarding the
details of each as mere modifications of a common type. "The spinal
column and the skull start from the same primitive condition, whence
they immediately begin to diverge." "It may be true to say that there
is a primitive identity of structure between the spinal or vertebral
column and the skull; but it is no more true that the adult skull is
a modified vertebral column than it would be to affirm that the
vertebral column is a modified skull." Taking the embryological facts,
he shewed that the skull arose out of elements quite different from
those of the vertebral column. The notochord alone is common to both.
The skull is built up of longitudinal cartilaginous pieces, now kn