Bones consist chiefly of =bone tissue=, but considered as organs they
present also an enveloping membrane, termed the =periosteum=, the
=medulla= or =marrow=, =vessels=, and =nerves=.
The architecture of bone can be studied best by means of longitudinal
and cross-sections. These show that the bone consists of an external
shell of dense =compact substance=, within which is the more loosely
arranged =spongy substance=. In typical long bones the shaft is hollowed
to form the =medullary cavity= (Cavum medullare).
[Illustration:
FIG. 1.—FRONTAL SECTION OF LARGE METATARSAL BONE OF HORSE, POSTERIOR
PART.
]
[Illustration: