igS GENERAL ORNITHOLOGY PART ii 



forward the structures which are more particularly concerned in the 

 classification of birds. I wish to give a fair account of the skeleton, 

 as osteological characters are of the utmost importance for the deter- 

 mination of natural affinities ; and to continue with some notice of 

 prominent features of the muscular, vascular, respiratory, digestive, 

 urogenital, and nervous systems, and organs of the special senses, 

 as the eye and ear. The tegumentary system has already been 

 treated at some length ; so has the osseous system, so far as the 

 bones of the limbs are concerned. What further I shall have to 

 say is designed merely as an introduction to avian anatomy, and 

 is supposed to be addressed to beginners. 



a. Osteology : The Osseous System, or Skeleton 



Osteology (Gr. omkov, osteon, a bone ; \6yo%, 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 ordinary connective tissue, such as that of most mem- 

 branes or any ligaments of the body. Bone-tissue presents a pecuUar 

 microscopic structure, in which it differs from teeth, as it does also 

 in not being developed from mucous membrane ; the substance is 

 called osteine, 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. •n-e.pi, peri, around, and 

 oo-Tiov), which is to bone what bark is to a tree. The bones col- 

 lectively constitute the osseous system, otherwise known as the 

 skeleton (Gr. a-KiXerov, dried, as bones usually are when studied). 

 The skeleton is divided into the endosheleton (Gr. eVSov, endon, within), 

 consisting 'of the bones inside the body ; and the exoskeleton (Gr. k^a, 

 exo, 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. a-KXrjpos, 

 sMeros, 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. a-rja-aij.r), sesame, a kind of pea) bones, so often found 

 in the ligaments and tendons about joints, are also 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, back- 



