134 GENERAL ORNITHOLOGY. 



a. Osteology : The Osseous System, or Skeletox. 



Osteology (Gr. oareov, osteon, a bone ; Xdyos, logos, a word) is a scientific description of 

 bono 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 ordinary connective tissue, such as that i>f most membranes or any ligaments of the 

 body. Bone tissue presents a peculiar microscopic structure, in which it diSers 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. nepl, peri, around, and otrreoi/), which is to bone what bark is to a tree. The 

 bones collectively constitute the osseous system, otherwise known as the skeleton (Gr. o-KeXeroi/, 

 dried, as bones usually are when studied). The skeleton is divided into the endoskeleton (Gr. 

 i'pdov, endon, within), consisting of the bones inside the body ; and the exoskeleton (Gr. f|, 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. o-kXtjpos, scleras, 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 bone). Sesamoid (Gr. arja-afiT], 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 skuU, 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 suture, or by movable articidation (Lat. articulus, a joint, dimin. of artus^ 

 a limb). In free articulations, the opposing surfaces are generally smooth, and lubricated 

 with a fluid called synovia. Progressive ossification often causes bones originally distinct to 

 coossify, that is, to fuse together ; this is termed ankylosis or anchylosis ; bones so melted 

 together are said to be ankylosed or ancliylosed (Gr. ayKvKaxns or ayxykaxris, the stifi'ening of 

 joints in a bent position). Thus all the bones of a bird's brain-box are auchylosed together, 

 though the box at first consists of many distinct ones ; and the detenniuation t)f 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 fi-om 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. KovhvKos, 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 caps of bone, as long as they are disunited, are called 

 epiphyses (Gr. eVi, epi, upon ; (^iais, j)husis, growth). Protrusive parts of bones have the 

 general name of processes, or aiJOiihyses (Gr. airo, apo, away from, and (f)vais); such have 

 generally no ossific centres, being mere outgrowths. But many i^arts of a vertebra, which are 

 called " apophyses," have independent ossific centimes. The progress of ossification is usually 

 rapid and efi"ectual. 



