152 CTENACANTHUS, A SPINE OF HYBODTS. 
ramuli are given nearly at right angles to t 
paren he tissue between equals about two-thirds of 
with the terminal branches of the neighbouring system. e 
diameters of these tubules average 3a's9th of an inch at their 
origin and the finer branches average +530% of an inch. There 
are no concentric layers of dense vascular tissue surrounding the 
central cavity near the root, but as we proceed upwards this 
concentric arrangement becomes observable. 
In the body of the spine the canals become slightly altered in 
character, those near the circumference being much smaller in 
layers, and those near the centre have also decreased in size to 
about the 200th of an inch but they are not surrounded by lamelle. 
The circumferential portion of the body has now, therefore, a 
superabundance of tissue over canals, but pe centre they 
are about equal. From all the canals seaipsvitvel tubes arise, 
but those near the centre give them off very sparin gly, while the 
vessels near the periphery do so xecedinehy abundantly ; the 
tubuli branch very freely and the ramifications anastomose ° 
quently with each other, so much so that where the tubules are 
numerous, as near the external surface, they fill the tissue be- 
tween the canals with a fine networ Surrounding each canal 
seoespdlsilee and in some parts is pierced by very large canals 
from which arise long but fine dendritic tubules. As we approach 
the apex the medullary cavity becomes smaller and smaller, and 
all tl area are surrounded by lamine and therefore smaller 
Such se 5 the Beir presented by sections of the spine of 
n d such are the characters observed when simi 
sections of Bey bodkea are examined, even the sizes of the tubules 
