OSSIFYING CARTILAGE. 
169 
blood-vessels for the nutrition of the bone are trans- 
mitted. These canals are larger on the inner or 
medullary surface of the bone than they are on the 
outer. Let the same section 
be next examined under a 
power of two hundred diame- 
ters, a concentric arrangement 
of laminae, as represented in 
Fig. 129, will be seen around 
each canal, and the black dots 
before alluded to will now pre- 
sent a s 
they are known as the lacunae, 
or bone-cells, and each con- 
sists of a central part or body, from which a number 
of minute tubes termed canaliculi proceed. The cana- 
liculi nearest to each Haversian canal open into it, whilst 
those more distant from the same canal, anastomose 
with the canaliculi of the next lamina ; those of the 
outer row of bone-cells do not anastomose with the 
canaliculi of neighbouring laminae, but nearly all bend 
back and join those of the preceding lamina. By this 
arrangement, a white line may be observed to sur- 
round the outer part of each of the concentric circles ; 
so that the hone may be said to be built up of a series 
of Haversian systems. If the same bone be divided in 
a vertical direction, as shown by Fig. 130, the course 
of the Haversian canals may be readily seen ; they run 
in parallel lines, and are connected together by oblique, 
pider-like appearance; 
FIG. 129 . 
Portion of a transverse section 
of a femur magnified 200 diame- 
ters. 
