OSSEOUS TISSUE. 
Fig. 454. 
_ Various forms of bone cells found in the bone of the 
| .. Boa Constréctor. 
Fig. 455. 
a a Se 
‘orm of bone cell in the common frog; b, bone 
tells from the crania of the common goldfinch ; 
€,form of bone cell in the sheep’s-head fish ; 
d, form of bone cells in the green-boned fish. 
y very definite enumeration, since no two 
will be found possessed of a like number of 
inching tubes. The general arrangement of the 
is radiate as regards the cells, which forms 
ircommon centre. This statement requires 
ne qualification, for not uncommonly a much 
feater number of tubes arise from one side of 
}cell than from the other, and these tubes all 
B51 
take one direction. \A tube after passing some 
little distance from the cell will in many in- 
stances divide, and each division pass on 
distinct from its fellow, equalling in size the 
pevent tube. Frequent anastomoses are effected 
tween different tubes arising from the same 
cells, but far more frequently between those 
which arise from neighbouring cells. So fire- 
quent are the connections that a free com- 
munication is established between the various 
cells and branching tubes throughout the 
substance of the bone. 
So numerous are the connections between 
the tubes, and immediately between the cells 
through the tubes, thata fluid introduced into one 
cell in a bone may find its way into every other 
cell of the bone. Indeed this does take place, 
though not from a single cell, yet from the 
surface of the bone. If, for instance, you place 
a bone that is dry, and opaque as a conse- 
quence of being dry, in spirits of turpentine, in 
a very little time this bone, before opaque, will 
become comparatively transparent, and this 
through the fluid having passed through the 
tubes into the cells. For, as will be shown, it 
is the tubes only that open upon the surface of 
the bone, either the external surface or the sur- 
face of the canals for vessels. Indeed, if a 
thin section of bone be taken and all moisture 
removed, and spirit of turpentine be added to 
it, when under the microscope, the passage of 
the fluid through the tubes may be seen, an ex- 
periment suggested by my friend Mr. Bowman. 
Besides this relation between the tubes them- 
selves and their cells, they have a very definite 
relation to the Haversian canals as well as to the 
free surface of the bone and also to the lamine. 
The position occupied by the cells is between 
the lamine, or on the surface of the lamine ; 
and where concentric lamine occur, as in the 
Haversian system, the cells are arranged in cir- 
cular lines between the laminz, each line of cells 
having as an exit common to it and the con- 
necting lamine the Haversian canal. The 
flattened sides of the cells are parallel with the 
circumference of the Haversian canal, while 
their greater diameter is in the direction of the 
circular line of the lamina, or with the length 
of the canal to which they belong. Bone 
cells so placed send out numerous tubes, which 
pierce the lamine at right angles and proceed in 
great numbers to the vascular canal, into which 
they enter, there terminating in an open mouth 
upon the surface ; thereby establishing a. con- 
nection of tube channels between the bone cells 
of the Haversian system and the canal of the 
system. (See fig.448.) Although these cellssend 
out many tubes in the above direction, yet others, 
though comparatively few, take an opposite 
course, and then establish by anastomosis a con- 
nection with the tubes of the surrounding bone 
cells. This is more particularly seen when we 
look upon a transverse section of an Haversian 
system; but if a section taken in the length of 
an Haversian system be examined, the tubes 
will for the most part be seen dividing the cells 
equally in point of number from every part of 
the circumference of the cell, and of course pro- 
ceeding in the length of the lamine between 
312 
