292 
NATURE 
[ Aug. 11, 1870 
true representatives of costal arches in this part of the 
frame? JI think that the external branchial cartilages 
of sharks and the branchial basket of the Lamprey will 
be found to be such, and therefore to belong to a quite 
different category from that to which the branchial arches 
of osseous fishes pertain. 
Again those azygos processes which descend from 
beneath the vertebral column in the region of the trunk, 
must be in the line of origin and suspension of the in- 
ternal lamella of the ventral plates of the embryo, and 
being related to them may be deemed to be hypaxial 
parts also, Their serial homologues often bifurcate, and 
are repeated serially in the caudal region by processes 
or distinct ossicles (chevron bones) protecting the caudal 
vessels, and which I deem to be hypaxial also. Professor 
Goodsir has demonstrated that in the crocodile such 
parts, at the root of the tail, lie within the backward pro- 
longation of the abdominal cavity, and the chevron bones 
or processes beyond that cavity in the same individual, 
are clearly the serial homologues of those within it. 
According to this view then, the vertebrate axial 
skeleton in its most generalised expression consists of an 
antero-posteriorly extended axis, bearing above it (1) a 
cylinder of efaazal parts, for the protection of the cerebro- 
spinal centres. This cylinder expands anteriorly, and has 
intercalated three sets of sense capsules, olfactory, optic, 
and auditory. Everything, whatsoever it be, outside the 
anterior end of this cylinder (the cranial capsule) is mor- 
phologically ox¢szde the skull, and therefore in such an 
essentially ex¢evnad position is the sella turcica, the ante- 
rior communicating artery, &c. 
2. From the axis of the skeleton diverge on each side 
more or less bifid Javaxial parts, tending to protect or 
surround the visceral cavity, or homologous with parts 
which do so tend. 
3. From the same axis descend hyfaxial farts, which 
parts attain their maximum of size and importance towards 
the two ends of the skeleton. At the anterior end they 
by their varied degree of development and coalescence, 
build up the frame-work of the face, the jaws, and the 
hyoidean structures. 
To this axial skeleton is added, in completely developed 
forms, two limb-girdles, each consisting of one upwardly 
and two inwardly and downwardly directed parts on each 
side. Two limbs, bilaterally symmetrical, are attached to 
each girdle, and a serial symmetry, bone answering for 
bone, exists between the anterior and posterior limbs of 
each side. 
Can the skeleton structure of these limbs be expressed 
in yet simpler terms? Professor Gegenbaur has attempted 
very ingeniously so to express it, considering the limb 
bones as differentiations of primitive similar offshoots 
from a chain of marginal’ fin bones or cartilages. But 
much as one would naturally wish to accept so tempting a 
theory, two obstacles at present oppose themselves. One 
is the presence of a radial ossicle answering to the 
pisiforme of the ulnar side. The other is the occasional 
presence, in fossil forms, of at least one whole chain of 
such ossicles. So that at present we can hardly in this 
respect venture upon a more generalised view of the 
skeleton than the one here adopted. 
This conception of the vertebrate skeleton takes little 
account of the mode of origin of skeletal parts—whether 
exogenous or autogenous, or of their segmented or un- 
segmented condition. But such considertaions have been 
neglected deliberately from a conviction of the completely 
subordinate importance of such conditions. The views 
here stated suggested themselves during the study of the 
skeleton as it exists in tailed batrachians; they have 
elsewhere been given at length, and their defence at- 
tempted, but it has been thought that a brief statement of 
them here might not be altogether unacceptable to some 
who are engaged in osteological inquiries. 
ST. GEORGE MIVART 
HOOKER’S BRITISH FLORA 
The Student's Flora of the British Islands. By J.D. 
Hooker, C.B., M.D., F.R.S., Director of the Royal 
Gardens, Kew. (London: Macmillan and Co., 1870.) 
OTWITHSTAN DING the number of British Floras 
already in existence, field-botanists have long la- 
mented the want of a text-book combining all the requi- 
sites for out-of-door work, unquestionable accuracy, 
clearly-expressed definitions, a good arrangement, and a 
portable form, Although the hand-books we have hitherto 
used have possessed one or other of these features in an 
eminent degree, no one has yet succeeded in uniting them. 
For accomplishing this difficult task the best thanks of 
every British botanist are due to Dr. Hooker. The pub- 
lication in quick succession of several works with a 
similar scope, may be taken asan indication of a reviving 
interest in British botany. Thirty years since, when the 
Linnean system of classification was still in use, a 
sufficient acquaintance with plants to enable anyone to 
give the Latin names of the species of their own districts 
was a fashionable acquirement, especially with ladies. The 
knowledge, however, was extremely superficial ; it con- 
sisted mainly in counting the number of stamens and of 
pistils, so as to determine the class and order, and of ob- 
serving the trivial specific characters of the foliage, colour 
and size of the flowers, &c., and was unaccompanied with 
the least real acquaintance with structural or physiological 
botany. An artificial classification like that of Linnzus, 
must always conduce to this result, and the ease with which 
plants can be named by such a method, is in itself an evil 
rather than an advantage. When we advance from an 
empirical toa natural system, in which the diagnoses of 
the orders depend on a variety of characters, some of 
them connected with minute details of structure, the gain, 
both to the learner and teacher, is immense. The learner 
is compelled to begin at the root of the matter, and to 
acquaint himself with the structure and physiological 
function of every separate organ, and with the different 
forms it may assume, before he attempts to name a plant ; 
and the teacher can no longer cram his class with that 
showy surface knowledge which is the bane of popular 
science teaching. The general adoption of the Natural 
system of classification was followed by a great falling- 
off in the ranks of amateurs. The number of real 
students of botany is now however, we hope, increasing 
day by day, and the substantial interest and instruction 
derived from the science are in proportion enormously 
augmented. 
The difficulties of the Natural system must be familiar 
to all teachers ; probably every lecturer has more than 
