28 ANATOMY OF THE RABBIT. 
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 (9) of a ground trans- 
verse section of the dried shaft of the femur. 
| Its dry weight consists of about one-third 
a 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 
ZAC. greatly branched spaces, the lacunae, in 
which in the natural condition the bone-cells 
are accommodated. On account of certain 
Bn differences in development, the lamellae are 
ie) disposed in different ways. Some are dis- 
Fic. 10. Divided femur : 5 ees 
of the rabbit; c.t., can. posed concentrically around longitudinal 
cellous tissue;  e., distal : 5 é 
epiphysis; e.l., epiphysial spaces, the Haversian canals, forming in 
line; m.c., marrow-cavity; 3 5 
s., shaft. 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 


