SECTIONII 



OSTEOLOGY 



Revised for the Fifth Edition 

 By peter THOMPSON, M.D., 



PROFESSOR OF ANATOMY IN THE UNIVERSITT OF BIRMINGHAM; EXAMINER IN ANATOMY, THE UNIVERSITY OP 



CAMBRIDGE; FORMERLY EXAMINER IN ANATOMY FOR THE UNIVERSITIES OP LONDON, ABERDEEN, MANCHESTER, 



DUBLIN AND FOR THE CONJOINT BOARD OF ENGLAND 



THE SKELETON 



THE skeleton forms the solid framework of the body, and is composed of 

 bones, and in certain parts, of pieces of cartilage. The various bones and 

 cartilages are united by means of ligaments, and are so arranged as to 

 give the body definite shape, protect from injury the more important delicate 

 organs, and afford attachment to the muscles by which the various movements are 

 accomplished. 



In its widest acceptance, the term skeleton includes all parts of the framework, whether 

 internal or external, and as in many of the lower animals there are, in addition to the deeper 

 osseous parts, hardened structures associated with the integument, it is convenient to refer to 

 the two groups as endoskeleton and exoskeleton or dermal skeleton, respectively. AH verte- 

 brate — i. e., back-boned — ^animals possess an endoskeleton, and many of them a well-developed 

 exoskeleton also, but in mammals, the highest group of vertebrates, the external skeleton, when 

 it exists, plays a relatively subordinate part. In most of the invertebrates the endoskeleton is 

 absent and the dermal skeleton alone is found. 



In man by far the greater part of the endoskeleton is formed of bone, a tissue of definite 

 chemical composition, being formed mainly of a gelatine basis strongly impregnated with lime 

 salts. 



The number of bones in the skeleton varies at different ages, some, which are 

 originally quite independent, becoming united as age advances. They are ar- 

 ranged in an axial set, which includes the vertebral column, the skull, the ribs, 

 and the sternum, and an appendicular set, belonging to the limbs. The following 

 table shows the number of bones usually distinct in middle life, excluding the 

 auditory ossicles: — 



Bones. 



» • 1 f The vertebral column 26 



Skeleton ^^^ ^^""^^ ^^ 



I The ribs and sternum 25 



Appendicular / The upper limbs 64 



Skeleton \ The lower limbs 62 



Total 200 



Several of the skull bones are compound, i. e., in the immature skeleton they consist of 

 separate elements which ultimately unite to form a single bone. In order to comprehend the 

 nature of such bones it is advantageous to study them in the various stages through which 

 they pass in the process of development in the fcetus and the child. 



It follows, therefore, that to appreciate the morphology of the skeleton — i. e., the history 

 of the osteological units of which it is composed — the osteogenesis or mode of development of 

 the bones must be studied, as well as their topography or position. 



Some bones arise by ossification in membrane, others in cartilage. In the embryo, many 

 portions of the skeleton are represented by cartilage which may become infiltrated by lime salts 

 — calcification. This earthy material is taken up and redeposited in a regular manner- 

 ossification. Portions of the original cartilage persist at the articular ends of bones, and, in 



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