412 
AN ESSAY ON CHRONIC PODOTROCHOLITIS. 
they attain the size of a hazel-nut. In this porous state the bone 
is exceedingly liable to fracture, and this accident is so very 
likely to happen from the caries being accompanied by friability 
( osteopsathyrosis ). 
While the navicular undergoes a loss of substance on the one 
side, it is very seldom that any newly-formed bony productions 
are perceived on the other. Osteophytes are developed on the 
posterior, superior, and inferior edge of the navicular bone ; and 
chiefly there appear spinous styloide, and diffuse osteophytes. 
The two first varieties arise from the posterior and inferior edge pro- 
longing themselves towards the coffin-bone, meeting with similar 
productions, which arise from this latter bone, and their union 
determines an adhesion between the coffin and navicular bones ; 
or else, these exostoses remaining free, present themselves under 
the form of sharp teeth. 
If the podotrocholitis has attained any great degree of chronicity, 
swelling, or puffing up of the coffin-bone will be found, as well 
as porosity of its projections. The synovial capsule at length par- 
ticipates in the morbid action : it becomes inflamed and thickened, 
and the fluid which it contains acquires a reddish hue. One pe- 
culiarity worthy of remark is, that at this period of the disease 
the anterior surface of the navicular retains its entire integrity ; 
at least I have never seen any alteration of it, nor any case in 
which the caries pervading the substance of the bone has reached 
this surface, has come under my notice. The cause of this pheno- 
menon is doubtless to be found in the great density of the compact 
bone ; the osseous tissue has, according to Richter and others, less 
tendency to inflammation, from its being more impermeable, and 
the calcareous salts being more concentrated in it. I must add, 
that in chronic podotrocholitis I have never happened to meet with 
any purulent secretion. It is true that Turner* speaks of ulcer- 
ation of the trochlean cartilage ; but he does not say that he found 
any pus. Besides, his language is equivocal ; perhaps by ulcer- 
ation he only means softening of the cartilage. In the bursal 
membrane a yellowish white flaky fluid is sometimes found, which, 
if examined superficially, might easily be mistaken for purulent 
matter : it has not, however, any of the characters peculiar to pus. 
Cloquet and others, not having always met with pus in the caries, 
have consequently admitted the existence of dry caries. It is 
this form which attacks the navicular bone, and it is perfectly 
distinct from necrosis as well as from osteoanahrosis , with -which 
it ought not to be confounded. 
Symptomatology . — Chronic podotrocholitis sometimes comes on 
* The Veterinarian. 1829, page 64. 
