fic work as a
medical student, the groundwork of all his knowledge was study of the
anatomy and physiology of man. Moreover, throughout the greater part
of his working life, he had more to do with the extinct forms of life.
The vertebrate animals, from the great facility for preservation which
their hard skeleton presents, as well as from the extremely important
anatomical characters of the skeleton, bulk more largely in the study
of palaeontology than does any other group. In each of the great
groups of vertebrate animals, in fishes, amphibia, reptiles, birds,
and mammals, Huxley did important work. Much of this is embodied in
his treatise on _Vertebrate Anatomy_, but to some particular parts of
it special attention may now be directed, as much because these serve
as excellent examples of his method of work as because of their
intrinsic importance.

The skull is the most striking feature in the skeleton of vertebrate
animals, and to the theory and structure of the vertebrate skull
Huxley paid special attention, and his views and summary of the views
of others form the basis of our modern knowledge. This work was put
before the public in the course of a series of lectures on Comparative
Anatomy given in 1863, while Huxley was Hunterian Professor at the
Royal College of Surgeons, and the beginnings of it were contained in
a Croonian lecture to the Royal Society in 1858.

The theory of the skull which held the field was known as the
vertebral theory. The great bulk of the nervous system of vertebrate
animals consists of a mass of tissue lying along the dorsal line of
the body and enclosed in a cartilaginous or bony sheath. The nerve
tissue is the brain and spinal cord; the sheath is the skull in front
and the vertebral column along the greater part of the length of the
animal. The brain may be taken simply as an anterior portion of the
nerve mass, corresponding in a general way to an expansion of the
spinal cord in the region of the anterior limbs and an expansion in
the region of the hind limbs, the latter indeed having recently been
shown in some extinct creatures to surpass the brain in size. In a
similar simple fashion the skull may be taken as an expanded anterior
part of the vertebral column, serving as an expanded box for the
brain, just as in the regions of the pectoral and pelvic expansions
of the cord there are similar expansions of the surrounding bony case.
We know now, from greater knowledge of its embryolo