ON THE VERTEBRATE SKELETON. 249 
Although my investigations of the fundamental type of the vertebrate 
skeleton were first made upon the class of fishes, where vegetative uniformity 
or irrelative repetition most prevails, and where, therefore, the type is least 
obscured by the modification of one part in mutual subserviency with an- 
other, I soon found that I should be led astray by confining my observations 
to fishes, and by borrowing my illustrations from that class. Comparison 
of the piscine skeleton with those of the higher animals demonstrates that 
the natural arrangement of the parts of the endoskeleton is in a series of 
segments succeeding each other in the axis of the body. These segments are 
not, indeed, composed of the same number of bones in any class or throughout 
any individual animal. But certain parts of each segment do maintain such 
constancy in their existence, relation, position, and offices, as to enforce the 
conviction that they are homologous parts, both in the constituent series of the 
same individual skeleton, and throughout the series of vertebrate animals. 
For each of these primary segments of the skeleton J retain the term ‘ verte- 
bra’; but with as little reference to its primary signification, as a part 
specially adapted for rotatory motion, as when the comparative anatomist 
speaks of a sacral vertebra. The word may, however, seem to the anthro- 
potomist to be used in a different or more extended sense than that in which 
it is usually understood ; yet he is himself, unconsciously perhaps, in the 
habit of including in certain vertebra of the human body, elements which he 
excludes from the idea in other natural segments of the same kind, influenced 
by differences of proportion and coalescence, which are the most variable. 
characters of a bone. Thus the rib of a cervical vertebra is the ‘ processus 
transversus perforatus,’ or the ‘radix anticus processus transversi vertebrae 
colli’*: whilst in the chest, it is ‘ costa,’ or ‘ pars ossea costz.’ But the ulna 
is still an ulna in the horse, although it be small and anchylosed to the radius. 
The osteology of man, therefore, cannot be fully or rightly understood 
until the type of which it is a modification is known, and the first step to 
this knowledge is the determination of the’ vertebral segments, or natural 
groups of bones, of which the myelencephalous skeleton consists. 
I define a vertebra, as one of those segments of the endo-skeleton which con- 
stitute the axis of the body, and the protecting canals of the nervous and 
vascular trunks: such a segment may also support diverging appendages. 
Exclusive of these, it consists, in its typical completeness, of the following 
elements and parts :— 
Te Kile ee ie cca ROSMAN esis Spine is 
Fig. 14. 
| Bm neural spine. 
zygapophysis. ~~. i 
lll. 
neurapophysis. 
© >....pleurapophysis. 
parapophysis. pe @ 
h rr 
~~~ heemapophysis. 
fps A 
zygapophysis. | 
je hemal spine. 
Ideal typical vertebra. 
* Soemmerring, De Corporis Humani Fabrica, 1794, i. p. 239. 
1846. 8 
