362 ANATOMY AND PHYSIOLOGY OF THE HORSe’s FOOT. 
bone, but without involving the polished face over which the 
tendon moves. This tendency seems to be more particu- 
larly limited to the lower half and middle portion of this sur- 
face, the compact and spongy tissues of the bone being at 
this early period unaltered. The infiltration appeared some- 
times to follow the direction of the fibres, and at other times 
the earthy matter seemed to be more especially deposited 
in and around the borders of the cartilage cells. In the 
majority of instances these cells looked as if primarily 
involved, the fibrous element only undergoing slight thicken- 
ing in lines and patches ; the cells, in this process of calcifi- 
cation, were sometimes enlarged to four or five times their 
ordinary size, but when not so magnified they were about the 
dimensions of bone-corpuscles, and offered all the characters 
of these, even to the presence of canaliculi projecting from 
their borders. In some of my microscopical preparations these 
canaliculi and lacunae are very conspicuous, and the change 
taking place in these points of the membrane is quite analo- 
gous, if it does not exactly correspond, to that observed in 
the transformation of temporary cartilage into bone. The 
cells are ossified in groups, and, with their numerous canali- 
culi, stand out in sharp relief from the healthy portions of 
the tissue. Each ossific mass constitutes a veritable minia- 
ture exostosis, viewed by the microscope. The animals from 
which these navicular bones had been procured were never, 
to my knowledge, lame in the fore feet during life. 
Other bones I have examined, obtained from horses which 
had been slightly lame in one or both fore feet for some time. 
In these the calcareous infiltration was more advanced, and 
one or more deposits of rough granular particles had taken the 
place of the fibrous membrane, and frayed or abraded the corre- 
sponding fibres on the anterior face of the tendon to a greater 
or less extent. In these specimens the surface of the compact 
tissue was, of course, involved, the osteophytic depositions 
having become fixed on it, and the superficial lacunae were be- 
coming obliterated; the cancellated structure was unaffected. 
In several old horses which had died through disease or acci- 
dent, and which had been more or less “ tender” on their fore 
feet for a variable period before death, this condition was very 
well marked. Two feet sent to me in November last by my 
lamented friend, the late Mr. Lawson of Manchester, showed 
these features very distinctly. On the lower face of the 
navicular bone of one foot a long thin deposit extended across 
the transverse ridge towards its lower extremity, and above 
this, on the ridge itself, and on each side, were apparently 
isolated granules disseminated in the enveloping membrane, 
