852 
which the cell is placed. As in the transverse 
section of the Haversian system these tubes 
that take the longitudinal direction are not 
seen, so in this section the tubes proceeding 
directly towards the Haversian canal are but 
badly shown. So many of the delicate tubes 
take the direction of the Haversian canals and 
enter it, that the parietes of each canal at first 
sight have a radiate ap nce, which has led 
some writers to describe a system of radiate 
tubes ing through some of the lamine, but 
the bate failed to trace their connection 
with the bone cells not far distant. When the 
cell with its radiating system of tubes is situated 
near the surface of the bone, the direction of 
the latter will be mostly towards that surface, 
unless indeed there is a vascular canal near at 
hand, in which case many will proceed towards it. 
Those cells which are placed in the connect- 
ing lamine send out their tubes tolerably 
equally in each division, anastomosing freely 
with the tubes coming from the cells belonging 
to the Haversian or superficial system of lamine, 
and so establish a communication between the 
cells of the three systems of lamine. The 
number of tubes and the size of the bone cells 
bear to each other no definite proportion ; thus 
a small cell may have many tubes while a much 
larger one has comparatively few. The number 
of the cells in a given space is subject to con- 
siderable variety, as well as the number of the 
radiating tubes, though generally the number of 
tubes will exist in inverse proportion to the num- 
ber of the cells. Thus in the crania of small 
birds the cells are of very frequent occurrence, 
while the tubes connected with each cell are but 
Section of a bone of an osseous fish. 
a, transverse section of Haversian canal; 6, longitudinal 
section of an Haversian canal with system of tubes opening 
into it, 
OSSEOUS TISSUE. 
I was disposed to hold a like opinion, but fi 
few. Again, in dense bones of quadrupeds and 
of man, the cells are less frequent, but the tubes 
of each cell far more numerous. 
Where the canals for vessels are very nu- 
merous the bone cells become more rare, and 
in some cases they are nearly absent,as shown in 
fig. 451. 
From the foregoing description it may be 
seen that the infinitely numerous tubes every- 
where connected amongst the cells, converging” 
at certain points and entering into cells, in fact 
form these cells ; that the cells are nothing more 
than many tubes coming toa point and le 
their individual parietes. ‘ 
In other cases where the tubes to each cell 
are not numerous, the cell itself may be cc 
pared to a dilatation of those tubes. This vies 
of the subject is borne out by the fact that ever 
in the human subject we find here and then 
tubes occupying the place of the cells and 
their radiating tubes, while in certain fish the 
cells are almost entirely absent and the simple 
tubes general. , 
In such instances the tubes hold the sa 
relation to the Haversian canals as do the bon 
cells where they exist. (See fig. 456.) 
The cells when seen by transmitted light, esp 
cially in a transverse section of bone, appé 
perfectly opaque; this has given rise to th 
opinion that they contain some am al 
and the fact that these same cells become tra 
parent when the bone has been subjected to 
action of acid, confirmed observers in t 
opinion, and that this salt was a salt of lim 
hen first these observations were commen 
therinvestigation has convinced me that asa Mm 
the cells are empty. I have seen, and that 
very frequently, cells which were 
viously without contents, and | 
observation may be repeated in ; 
bone where the cells are toler 
large by making a section in 
length of bone, and so L 
the direction of most of the Haver 
canals. By making such a sec 
you expose the cells in their la 
diameter, when they may be seen 
whereas if cut through in theirm 
diameter they are so deep tha 
produce complete interference of] 
- and so seem black, as though 
with some opaque substance. 
Again, if turpentine or thin Cs 
balsam be added to a section | 
dry beforehand, the dark cells 
become filled with turpentine © 
sam, and so become transparent 
The function performed by th 
cells is no doubt that of eiret 
Atmospheric pressure would 
them from remaining empty, 
their openings are always U 
surface where there are blood! 
the fluid portion of the blood 
bably carried into them. Sap 
them once filled with rp sang 
the varying density of ood 
would produce a slow kind of 
