d that there was (1) a histological and (2)
a morphological difference between the two categories of bones. The
histological development of the two kinds was different, but this
difference was not sufficient to establish a morphological distinction
between them, a distinction in their anatomical _Bedeutung_. The true
morphological distinction between them was their development in
different skeleton-forming layers. Membrane bones were developed in
fibrous tissue lying between the skin and the deep layer which formed
the primordial cranium, and it was this formation in a separate layer
that gave them a different morphological significance from the bones
formed directly in the deep layer. Koelliker's distinction, therefore,
was between the bones formed in the primordial cartilaginous cranium on
the one hand, and the superficial ossifications in fibrous tissue on the
other hand. The cartilaginous cranium in Koelliker's opinion was formed
upon the vertebral type, and the membrane bones were accessory. This, at
least, was his opinion in 1849. In 1850, after Stannius had shown that
membrane bones occurred as integral parts of the vertebrae in certain
fish, he modified his view of the membrane bones, and admitted them, at
least in some cases, as constituents of the cranial vertebrae.

On this morphological distinction of membrane and cartilage bones future
comparative osteology was to be based:--

"My sole aim is to state again the principle upon which comparative
osteology is to be based and extended, and this is that first place
should be assigned to anatomical considerations, and among these to the
manner of origin of the whole bone in relation to the skeleton-forming
layers" (1850, p. 290).

The homologies established by this new principle might run counter to
the homologies indicated by the study of adult structure. "Thus, for
instance, although the lower jaw in position, function, form and shape,
appears to be the same bone throughout, yet it must be admitted that it
shows a difference in the different classes. In Mammals and Man it is an
entirely secondary bone (an extremity according to Reichert), in Birds,
Amphibia and Fishes only partially so, for its articular belongs to
Meckel's cartilage and is accordingly analogous to a rib; indeed, in the
Plagiostomes, etc., the whole lower jaw along with the articular is a
persistent Meckel's cartilage" (p. 290, 1850).

So, too, the supraoccipital in man cannot be fully homol