254 
LIFE, IN ITS HIGHER FORMS. 
running longitudinally through the animal. These pieces 
are called vertebral. The best way to study a vertebra is to 
take that of a Fish, — one of the joints from the backbone 
of a Cod for example, since in this Class we find it most 
simply and yet most perfectly developed. We thus per- 
ceive that it is composed of several parts : — 1. The central 
cylinder ; 2. the superior arch , formed by two sloping side 
pieces, between which the spinal marrow passes ; 3. the 
superior spinous process, projecting upward from the union 
of these pieces ; 4. the two lateral processes ; 5. the infe- 
rior arch, formed as the superior is, protecting great blood- 
vessels; 0. the inferior spinous process, pointing downward. 
A number of the vertebra; at the fore part of the column 
are so far modified in shape and proportion of parts as to 
be identified only by close study and comparison. They 
constitute the skull, a capacious chamber of bone formed 
to contain the brain, which is but the aggregation of seve- 
ral pairs of ganglia greatly developed. 
In front of these bones there is placed another series, 
arranged in pairs, constituting the face ; some of these are 
excavated into cavities to protect the organs of sense, and 
others form the jaws, Arc. 
These may all be considered as integral parts of the 
vertebral column ; but besides these, there are important 
accessories yet to bo noticed. First, there are a number 
of slender bones, which are articulated to the transverse 
processes of the vertebras, and arch outwards and down- 
wards. They form two series : 1. The hyoid arches, 
which spring from the skull : these are minute in the 
human skeleton; but in some animals, especially in Fishes, 
they are large and important, forming the great frame- 
