28 



Anatomy of the Rabbit. 





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costal cartilages of the ribs, and a portion of the nasal septum; 

 it is also found uniting the basal bones of the skull. In the embryo, 

 however, it forms the entire skeleton, with the exception of a small 

 portion which, as described below, is formed of membrane bone. 

 In the course of development, except in the situations indicated, 

 the cartilage is replaced by bone. 



Bone is a compact, resistant, but yet 

 somewhat elastic tissue, possessing much 

 greater strength than cartilage, and therefore 

 forming a more perfect skeletal support. As 

 indicated below, its appearance as a tissue 

 differs somewhat according to its mode of 

 formation. The more typical structure (intra- 

 membranous bone) is illustrated in the 

 accompanying figure (q) of a ground trans- 

 verse section of the dried shaft of the femur. 

 Its dry weight consists of about one-third 

 animal matter and two-thirds mineral matter, 

 the latter being chiefly calcium phosphate. 

 The bone materials are deposited in layers 

 or lamellae, which are comparable to highly 

 modified white fibres of fibrous connective 

 ti-sue. The lamellae enclose between them 

 greatly branched spaces, the lacunae, in 

 which in the natural condition the bone-cells 

 are accommodated. On account of certain 

 differences in development, the lamellae are 

 disposed in different ways. Some are dis- 

 posed concentrically around longitudinal 

 spaces, the Haversian canals, forming in 

 this way the so-called Haversian systems. 

 The canals are occupied in the natural con- 

 dition by bloodvessels. Others of them, the interstitial lamellae, 

 are disposed in a somewhat parallel fashion between the Haversian 

 systems; while a third series, the circumferential lamellae, 

 are disposed in a parallel fashion with respect to the periphery or 

 the internal surface of the bone. In the natural condition the bone 

 is enclosed except on its articular surfaces by a layer of connective 



Fig. io. Divided femur 

 of the rabbit; c.t., can- 

 cellous tissue; c, distal 

 epiphysis; e.l.. epiphysial 

 line; m.c, marrow-cavity; 

 s., shaft . 



