24 



ANATOMY OF THE RABBIT 



ing figure (11) of aground transverse section of the dried shaft of a ra- 

 dius. Itsdry 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 

 tissue. The lamellae enclose between them greatly branched spaces, 

 the lacunae, which connect with each other and with the outer 

 surface of the bone by very delicate canaliculi and in which during 

 life the bone cells are accommodated. In the natural condition, 

 each bone is enclosed, except on its articular surfaces, by a layer of 

 connective tissue, the periosteum, derived in the case of replacing 

 bones from the perichondrium of the original cartilage. During 

 the period of growth, this membrane contains numerous bone- 

 forming cells, the osteoblasts, through the activity of which the 

 bone lamellae are deposited. 



Compact bone of the adult develops in the embryo from spicules 

 which become connected to form a spongy network, the marrow 

 spaces in which are then gradually reduced by deposition of 

 successive layers of bone-matrix until they 

 appear as canals, the Haversian canals, sur- 

 rounded by concentric lamellae. The con- 

 centric series of bone-cells and lamellae con- 

 stitutes a Haversian system and the canal 

 often contains an artery and a vein with a 

 little connective tissue. Between the Haver- 

 sian systems there may be bands of inter- 

 stitial lamellae and over the outer and inner 

 surfaces, parallel with them, zones of circum- 

 ferential (respectively periosteal and endos- 

 teal) lamellae. 



Bone may be formed either with or without 

 a cartilage basis, being known in the former 

 case as cartilage or replacing bone, in the lat- 

 ter as membrane or derm bone. The for- 

 mer is the more usual, replacing units of 

 the primary cartilage skeleton, which ap- 

 pears earlier in the embryo. This it does 

 both by surrounding and by invading the units 



Fig. 12. Inner surface of 

 proximal end of a dried 

 femur of a rabbit divided 

 longitudinally, ct, cancel- 

 lous bone in proximal 

 epiphysis; el, epiphysial 

 line; me, marrow cavity of 

 shaft, enclosed by compact 

 bone. 



