824 
Elements of a vertebra (after Owen ). 
encrustment of bone as to resemble a single 
mass; and in both the Rays and Sharks there 
are many more lamine enclosing the x sem 
canal than there are bodies of vertebra, bony 
plates being developed over the junctions of 
vertebral centres with each other as well as in 
the usual situation,—a circumstance which might 
at first sight seem to militate against the views 
adopted by modern physiologists concerning 
the elemental constitution of this part of the 
body, but from which, in reality, no legitimate 
inference is deducible, seeing the extremely 
confused and incomplete progress of ossification 
in all the cartilaginous Fishes. 
Advancing to the osseous Fishes, such con- 
fusion no longer exists, and every vertebra 
assumes a precise form corresponding with the 
particular uses assigned to it in the region 
which it occupies. Before, however, proceed- 
ing further, it behoves us to resolve an isolated 
vertebra into the primary elements of which it 
may itself be made up, and then we shall 
understand how all the varieties of shape pre- 
sented by these bones are easily obtainable by 
the simple exaggeration, diminution, or suppres- 
sion of some of the elements composing it. 
Geoffroy St. Hilaire was the first anatomist 
who pointed out the importance of thus analysing 
the different portions of the osseous system, 
and the views which were promulgated by that 
learned writer were generally adopted until 
Professor Owen, in the course of his researches 
concerning the composition of the skeletons of 
extinct British Reptiles, was led, as we think 
very justly, to modify considerably the views 
which had been previously entertained upon this 
OSSEOUS SYSTEM. (Comp. Avat.) 
Fig. 433. 
subject; we cannot therefore do better than lay 
before the reader the conclusions deduced by 
Professor Owen from a very elaborate and exten- 
sive survey of the various forms of the skeleton. 
“ A vertebra,” says Professor Owen,“ may 
be traced through its various degrees of com- 
plication, either during the fs veapect stages 
of its developement, or by taking permanently- 
formed vertebre of different es of com- 
pany in different animals; or in many instances — 
y comparing the vertebrae in different parts of 
the spine in the same animal.” 
The terminal vertebre of the tail in most — 
species exhibit the simplest condition of these 
bones. The most complicated vertebre are 
those of the lower part of the neck of certain — 
birds, as the Pelican, or at the beginning of 
the tail of a Python or other large Serpent. ‘ 
The parts or processes of such a vertebra 
may be divided into autogenous, or those which 
are independently developed in separate carti- 
lages, and exogenous, or those which shoot out 
as continuations from these independent con-— 
stituents. The autogenousor true elementsare— 
1. The centrum or body of the vertebra’ 
(fig. 433, d,) which in Mammalia, as Cuvie 
has observed, is complicated by two epiphyses. 
2. Two superior lamine (6, 6) developed 
protect the great nervous cord which rests on 
the upper surface of the centrum, and which 
Professor Owen therefore proposes to cal 
Neurapophyses. 
3. Two inferior lamine (e, e€) develop 
generally to protect the great bloodvessels on 
the under surface of the centrum, and which 
may be called Hemapophyses. a 
4. The superior spinous process (a) which i; 
connected and gerferally anchylosed with the 
distal extremities of the neurapophyses, 
forms, in conjunction with those processes, th 
superior arch of the vertebra. 
5th. An inferior spinous process which i: 
connected and commonly anchylosed with th 
distal extremities of the Hemapophyses, for 
ing in conjunction with these a chevron ot 
V-shaped bone. . 
To the category of autogenous vertebr 
pieces likewise belong the ribs (ce), 
are generally anchylosed to the other vy I 
elements in the cervical, sacral, and cai 
vertebra of the warm-blooded oe class 
The propriety of regarding the ribs as ver 
bral elements is well illustrated in the y 
Saurus, in the cervical, sacral, and caut 
vertebre of which they have been general 
described as transverse processes, although th 
are separate bones. f 
True transverse processes are always exog 
nous, or mere projections from the centrum 
the neurapophyses, and are of secondary imp 
tance. They are of two kinds, superior a 
inferior ; both are present in the cervical ¥ 
tebree in most classes of the vertebrated anima 
the inferior transverse processes alone are dey 
loped in Fishes. aa 
The oblique or articulating processes are als 
exogenous, and may be developed either fro 
the neurapophyses or the base of the supe 
spines of the vertebra. ¥ 
As in other complicated bones resulting fro 
