4 . REMARKS ON THE FIGURES OF PLATE LIL. 
ness of function, or a oneness of essential character, in 
any respect or in any measure whatsoever. They have 
“again, on the other hand, passed heedlessly by that line 
of fluxion which Nature establishes for relationary struc- 
tures, and hence have read as specific distinctnesses those 
creations which Nature always transforms in the same 
place, through the phaseal development of the one animal 
body, as well as through the graduated series of an 
animal kingdom. They have confounded the dermal 
skeleton with the osseous skeleton, notwithstanding the 
difference of place, of function, and of structure; while 
they have overlooked that close analogy which reigns 
between the fibrous, the cartilaginous, and the osseous 
skeleton, structures which may be said to evince such a 
serial and connected argument, both as to place and 
function, that the same blood-vessels are the agents of 
their successive deposition; and the stages of the ossific 
process from fibrous to cartilaginous, and thence to bony 
tissue, are so enchained together, that these express a 
oneness in every sense of that word excepting that of 
time. A general view of the graduated scale of the animal 
kingdom will render it manifest that two or more animal 
structures, specifically distmet from each other, such as 
dermal and osseous tissues, do here and there assume a 
greater or lesser importance for several classes of forms, 
according to circumstance and requisition. Many of the 
lower classes of animals produce a dermal outer skeleton 
to the exclusion of the osseous internal fabric; and this 
point of transition, from the absence of the osseous 
skeleton to the presence of the dermal skeleton, is occupied 
by the Sepiz. These animals are examples of where a dermal 
structure assumes the office, in some degree, of an osseous 
structure; but still, both these distinct structural species 
remain as evidently unallied to one another, and can with 
as little reason be designated the same structural ens, as 
can the scaly armour of an armadillo be identified with 
its osseous framework. That structure which is deposited 
internally in one class of animals, such as the osseous 
skeleton, cannot have been laid externally for another 
class of animals, in the new character of a .dermal 
skeleton; and therefore these structures are to be 
accounted as distinct from each other, in two classes of 
animals, as the ike structures are held distinct in the one 
animal form.* But the phaseal metamorphosis from 
ligament to cartilage, and thence to bony tissue, is a 
process carried on internally at the same fixed localities ; 
and as we discover that these several transition deposits 
occupy, from time to time, the one place, so therefore do 
they express the one design of an endo-skeleton, to whose 
development and form of a unity rendered propor- 
tionally various, we confine our observations. Where 
osseous tissue now stands, there cartilaginous and fibrous 
structure once stood; where cartilaginous tissue now is, 
there fibrous tissue once was, and here osseous tissue will 
be; and where fibrous tissue now appears, there carti- 
laginous and osseous tissue will appear. ‘This is the 
history of the natural skeleton as it passes through the 
phases of development for the one animal body, and it is 
most true that those stages of the ossific process which are 
transitionary for the one animal skeleton of mammalian 
cast, are holding permanently for the special designs of 
other endo-skeletons throughout the four classes of animals. 
This subject expresses, no doubt, an intimate bearing on the 
law of endo-skeleton variation, and proves to the searcher 
after analogies that the unity of this form, to which ana- 
tomical science would fain direct attention, can never be 
embodied unless by taking full account of the ossific process. 
The variety which has place in the progressive growth 
of the mammalian skeleton form is mainly owing to the 
difference as to time in which several parts of this struc- 
ture present of one or the other of the three phases of the 
ossific process. As this cannot be denied, let us take 
footing upon this sure groundwork of a fact, and we shall 
find, while we look around us at the creative operation of 
the natura throughout an animal kingdom, that fact will 
cleave to fact, and all facts in mass will body forth the 
evidence that all variety apparent amongst the skeleton 
figures of mammifers, birds, reptiles, and osseous fishes, is 
attributable to the natural rule, viz., that various parts of a 
whole quantity present in one or other of the three stages 
of the ossific process. As in the human skeleton that 
part which, in embryonic life, was of cellular material, 
and destined, through after phases, to assume the carti- 
laginous and the osseous form, so in the plurality of the 
four classes of animals, their variation depends upon this, 
viz., that the part which is fibrous or cellular in one cast 
of formation, and which gives it its special and fitting 
character, has become, in another form, of cartilaginous 
structure, and in another, of osseous texture. 
The mechanical fitness of skeleton form is not that rule 
of development whereby a unity or whole quantity can 
ever be summed together out of comparative method ; 
and while the fact is openly manifested, that this mecha- 
nical design, throughout not only the phaseal growth of 
the one being, but also throughout the graduated scale 
of the four classes of osseous skeletons, is dependent upon 
those skeleton parts which Nature gives fixation to in 
either the fibrous, cartilaginous, or osseous forms; then 
there is every good reason to conclude that skeleton unity 
or the whole can no more be discerned according to those 
parts alone which are of the osseous phasis in several forms, 
than it can be read in the comparison of those parts which 
are of cartilaginous condition alone, or of those which are 
of fibrous cast alone. The osseous material of any animal 
body no more constitutes the entire skeleton form than 
does either the cartilagmous material or that which 
presents of fibrous character. If we limit our ideas of 
the skeleton fabric to parts which are of osseous growth, 
we will fall as far short of recognisimg the whole quantity 
of unity as we will fail of summing together the full 
evidence of the law which, by degrading several regional 
parts of this whole form, establishes all special varieties. 
* “Tia loi de la continuité porte que la nature ne laisse point de vide dans l’ordre qu’elle suit, mais toute forme ou espéce n’est pas de toute 
ordre.”—Leibnitz, Guvres Philosophiques. 
Now. Essais, §¢., liv. iii., p. 267. 
