OSTEOLOGY. 



By G. D. THANE. 



THE SKELETON. 



THE skeleton or solid framework of the body is mainly formed of the bones, but 

 is completed in some parts by the addition of cartilages. The bones are bound 

 together by means of ligaments, and are so disposed as to support the softer parts, 

 protect delicate organs, and give attachment to the muscles by which the different 

 movements are executed. 



In the lower animals the term skeleton has a wider signification than in man, 

 comprehending two sets of parts, viz., 1st, those of the endoskeleton, or the deeper 

 osseous and cartilaginous framework which corresponds to the human skeleton ; and 

 2nd, those of the exoskeleton, or dermal skeleton, comprising the integument and 

 various hardened structures connected with it. All vertebrate animals possess an 

 eudoskeleton ; but in some of them the exoskeleton attains greater proportions 

 than in others, and is combined by means of hardened parts more f ully with portions 

 of the endoskeleton. In most invertebrate animals the dermal or exoskeleton alone 

 exists. 



In man, as in the higher vertebrates, the greater part of the endoskeleton is 

 formed of bone, a calcified animal tissue, which, when freed by putrefactive macera- 

 tion from its fat and various soft adherent parts, and subsequently dried, is capable 

 of remaining unchanged for a very long period of time. It is customary and con- 

 venient thus to study the bones chiefly in the macerated and dried state, that is, 

 deprived of their accessory soft parts. 



The accessory soft parts connected with the fresh bones consist chiefly of the 

 external fibrous and vascular covering termed periosteum, and of the medulla, 

 marrow or fat, which fills their larger internal cavities. The bones are permeated 

 by blood-vessels, and they are provided also with absorbent vessels and with nerves 

 in small quantity. 



The ends of the bones, when jointed moveably with others, are covered by a thin 

 layer of dense permanent cartilage, called articular cartilage; and the adjacent 

 bones are united together by fibrous ligaments which may be considered as con- 

 tinuous with the periosteum covering the rest of the bones. In some instances 

 distinct bones are directly united by means of ligament or cartilage without any 

 joint-cavity intervening. Thus the osseous system as a whole may be considered to 

 be enveloped by a fibrous covering. 



The bones are originally formed by a process termed ossification from soft sub- 

 stance. This process commences in the greater number of bones in cartilage ; in 

 some it begins in fibrous tissue or membrane ; and in all instances the farther 

 growth of the bone substance takes place largely in the latter way. The deposit of 

 bone begins generally at one spot, which is therefore called the primary centre of 

 ossification ; but there may be several of these from the first. The main part of the 

 bone thus formed from the primary centre is sometimes named the diaphysis. In 

 most bones, after considerable advance in growth by extension from the primary 



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