; 
850 
have to be considered in relation to their num- 
ber, their size, and the parts which they contain. 
The number of canals in a given s is 
— a little variable, but this variation will 
regulated in some degree by the situation of 
the bone, but more especially by the age of the 
bone. Thus the transverse section of the femur 
of a human feetus of seven months will present 
many more canals than a section of equal mea- 
surement from the femur of an adult. 
In certain fish of which the Scarus is a spe- 
cimen, the Haversian canals are extremely nu- 
merous, so that bone cells become unnecessary, 
for here we find very few indeed, and in ‘some 
sections none. ( fig. 451.) 
Fig. 451. 
Section if bone from the Scarus; showing that where 
the Haversian canals are very numerous the bone 
cells are absent. 
The size of the Haversian canals takes a con- 
siderable range, varying from the yj,rd to the 
sisth of an inch, as stated by Mr. Smee. In the 
young subject they seem larger than in the old. & 
But by far the most marked difference in size of § 
these canals is to be observed in the antlers of 
the stag at different periods of their growth. f 
At an early period of the existence of the antler, 
the vascular canals are large and numerous, 
while at the time of their completion in size 
the canals are less numerous in an equal 
space, and very small: indeed many seem all 
but iabnended The density of bone is pro- 
duced more by the small size of the canals than 
by their comparative infrequency, though un- 
doubtedly they are less frequent in the compact 
bone, as that composing the shafts of long bones. 
In tracing individual canals, it will be found 
that the majority maintain the same size as far 
as we can follow them. This is not, however, 
observable in all. If a large canal be taken 
where it first enters the substance of the bone, 
it may be found giving off branches from time 
to time in various directions, and then again 
sending off smaller branches, which anastomose 
freely with each other, often joining at right 
angles. 
Although it is very easy to trace a large 
canal pervading a bone, and then dividing from 
time to time into smaller ones, I have never 
been able to satisfy myself that these small 
canals again unite to form a second large canal, 
and thus to leave the bone. I am therefore 
led to the opinion that such does not occur, 
but that the small even-sized canals open and 
OSSEOUS TISSUE. 
give exit to their vessels upon the surface of the 
bone generally, while the large canals give 
entrance to arteries. 
The Haversian canals undoubtedly give pas- 
sage to bloodvessels, which is their principal, 
if not their only purpose. Whether they con- 
tain one or more vessels seems to admit 
of a little doubt. Dr, Carpenter, in his work 
on Physiology, states that they contain an 
artery and vein. From my own observation I 
= not able 2 confirm his view. Indeed I am 
i d to the opinion that they give passage 
to nee vessel ain that du ieone canals 
which are found entering the bone an 
artery ; that it divides from time to time after the 
manner of the canals described ; and that the 
vessels emerge again from the surface of the 
bone as capillaries. This branch of the ~—— 
requires some further investigation. The 
going observations apply only to di bone. 
hare bone ip. Goneaiielen for the reception of 
fat, the vessels occupy but a small space in the 
cancelli. 
uscles or cells of bone; also 
Of the corp 
called /acune by Dr. Todd and Mr. Bowmar 
The so-called corpuscles are nothing more 
than small cells existing in the substance of th 
tissue, and might with ory be called bone 
cells. Some anatomists have designated them 
Fig. 452. 
Section of a flat bone, showing the bone cells in 
granular tissue, 
calcigerous cells, from the supposition t 
they contain in their interior an amorphi 
salt of lime. That this view is incorrect } 
be subsequently shown. The cells cannot 
described as having any definite ur ur 
shape or size. The general form is a | 
pressed oval, though not unfrequently the 
circular, but flattened from side to side. A 
they are sometimes almost triangular 
outline, while in other instances they appre 
linear shape. These are the most comm 
rieties ofoutline to which the bone cells are 
ject ; as they occur in the bones of man an 
higher animals. But connected with 
are numerous delicate branching tubes, 
slightly dilated as they enter the cells. 
number arising from each cell does not 
2 
