134 GENERAL ORNITHOLOGY. 
a. OSTEOLOGY: THE OSSEOUS. SYSTEM, OR SKELETON. 
Osteology (Gr. daréov, osteon, a bone; Adyos, logos, a word) is a scientific description of 
bone in general and of bones in particular. Bone consists of an animal basis or matrix (Lat. 
matrix, a mould) hardened. by deposit of earthy salts, chiefly phosphate of lime. Bone is 
either preformed in the gristly substance called cartilage (Lat. cartilago, gristle), and results 
from the substitution of the peculiar osseous tissue for the cartilaginous tissue, or it is formed 
directly in ordimary connective tissue, such as that of most membranes or any ligaments of the 
body. Bone tissue presents a peculiar microscopic structure, in which it differs from teeth, as 
it does also in not being developed from mucous membrane; the substance is called ostein, 
as distinguished from dentine. Though very dense and hard, bone has a copious blood-supply, 
and is therefore very vascular ; the nutrient fluid penetrates every part in a system of vessels 
called Haversian canals. In the natural state bone is covered with a tough membrane called 
periosteum (Gr. epi, pert, around, and éoréov), which is to bone what bark is to a tree. The 
bones collectively constitute the osseous system, otherwise known as the skeleton (Gr. oxederdy, 
dried, as bones usually are when studied). The skeleton is divided into the endoskeleton (Gr. 
évdov, endon, within), consisting of the bones inside the body ; and the exoskeleton (Gr. €€, ex, 
out of), or those upon the surface of the body, of which birds have none. Certain bones 
developed apart from the systematic endoskeleton, in fibrous tissue, are called scleroskeletal 
(Gr. cxAnpés, scleros, hard), as the ossified tendons or leaders of a turkey’s leg, the ring of 
ossicles in a bird’s eye (an ossicle is any small boue). Sesamoid (Gr. onoayn, sesame, a 
kind of pea) bones, so often found in the ligaments and tendons about joints, are probably 
best considered scleroskeletal. The endoskeleton is divided into bones of the axial skeleton, 
so called because they lie in the axis of the body, as those of the skull, backbone, chest, 
pelvis, and shoulder-girdle ; and of the appendicular skeleton, including bones of the limbs, 
considered as diverging appendages of the trunk. The skeleton is jointed; bones join 
either by immovable swtwre, or by movable articulation (Lat. articulus, a joint, dimin. of artus, 
alimb). In free articulations, the opposing surfaces are generally smooth, and lubricated 
with a fluid called synovia. Progressive ossification often causes bones originally distinct to 
codssify, that is, to fuse together; this is termed ankylosis or anchylosis ; bones so melted 
together are said to be ankylosed or anchylosed (Gr. dyktAwois or ayxvAwors, the stiffening of 
joints in a bent position). Thus all the bones of a bird’s brain-box are anchylosed together, 
though the box at first consists of many distinct ones; and the determination of such osseous 
elements or integers in compounded bones is a very important matter, as a clue to their 
morphological composition. The names of most individual bones, chiefly derived from the 
old anatomists, are arbitrary and have little scientific signification; many are fanciful and mis- 
leading; bones named since anatomy passed from the empiric stage, when it was little more 
than the art of dissecting and describing, however, have as a rule better naming. The shaft 
of a long bone is its continuity: the enlargements usually found at its extremities are called 
condyles (Gr. xkév8uX0s, kondulos, a lump, knot, as of the knuckles). Points where ossification 
commences in cartilage or membrane, are ossific centres, or osteoses ; valuable clues, usually, 
to the elements of compound bones. But ossification of individual simple bones may begin in 
more than one spot, and the several osteoses afterward grow together. This is especially the 
case with the ends of bones, which often make much progress in ossification before they unite 
with the shaft or main part; such eaps of bone, as long as they are disunited, are called 
epiphyses (Gr. eri, epi, upon; pious, phusis, growth). Protrusive parts of bones have the 
general name of processes, or apophyses (Gr. and, apo, away from, and dvous); such have 
generally no ossifie centres, being mere outgrowths. But many parts of a vertebra, which are 
called ‘‘ apophyses,” have independent ossific centres. The progress of ossification is usually 
rapid and effectual. 
