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110 ANATOMY.

The Anterior Portion, or splieno-ethmoid portion, forms in front of
the notoehord, along the trabeculee cranii, and includes the matrix of
the presphenoid and the septal-ethmoid cartilage. It extends forward
to the anterior portion of the nasal cartilage and the aperture for the
external nose.
Behind the nasal cartilage the trabeculse cranii unite to form the
etlimo-vomerine cartilage, which forms part of the nasal septum. Later-
ally, the presphenoid cartilage, the matrix of the orbito-sphenoid, the
lesser wings of the sphenoid bone, and the optic foramen are developed.
The Posterior Portion, or occipito-sphenoid portion, is formed from
that part of the notoehord situated behind the pituitary fossa, and, in
conjunction with the surrounding tissue, contains the matrix of the basi-
sphenoidal cartilages. This portion also extends laterally, and forms
the matrix of the exoccipital and periotic mass of cartilage which sur-
rounds the primary auditory vesicles.
The greater part of the occipito-sphenoid portion prolongs forward,
and extends below the posterior and middle primary encephalic vesicles,
and the matrix for the great wing of the sphenoid process derived from
the basisphenoid.
It will thus be seen that the base of the brain-case, extending to the
most anterior portion of the cartilage of the nose, is a foundation of
cartilaginous tissue, and all the bones—speaking of them as they are
divided by the comparative anatomist—arising immediately from this
foundation to form the base of the brain-case are cartilaginous bones.
The remainder of the bones of the brain-case, or those formed on each
side of the chorda dorsalis and trabeculae cranii, such as the interpari-
etals and squamo-zygomatics, are developed in membrane. These mem-
branous bones are claimed by Kolliker to be of dermal origin ijnd to
belong to the group of investing bones.
The facial bones, except the inferior turbinated, are developed in
membrane, similarly to the tabular bones of the head ; and as the mem-
branous bones of the cranial vault articulate with the cartilaginous
bones which form the base of the brain-ease, so all the membranous
bones of the face articulate from below with this same cartilaginous
foundation. The inferior maxilla would seem to be an exception to
this membro-cartilaginous articulation ; but in the early stages of its
development it is connected, through the cartilage of Meckel, with the
periotic bones.
The Face.—The bones of the brain-case, formed from the notoehord
and trabeculte, are in an advanced state of development before the
facial bones commence to be built. To such an extent is this the fact
that the dermoid structure (the skin) lies almost in contact with all
that portion of the head below and anterior to the notoehord, and
there is at this time no opening to the upper portion of the aliment-
ary canal.
The facial bones arise from the under surface of the base of the
brain-case from certain ]n'ocesses, and push outward and downward,
leaving a layer of dermoid tissue on their inner as well as their outer
surfaces. This dermoid tissue becomes the mucous or epidermoid
(epiblastic) lining of the mouth, nasal cavities, and all the internal sur-