208 MR. J. B. SUTTON ON DISEASES OF fApr. 20, 
suffer at some period of their life from those troublesome thickenings 
of the skin of the feet and toes known as corns. Structurally a 
corn consists of thickening of the epidermis, due to pressure of an 
intermittent character, often the result of badly fitting boots. In 
many cases a small sac containing fluid may be detected between 
the thickened epidermis and the deeper tissues ; this sac is techni- 
cally termed a bursa. In others the bursa is replaced by loose 
connective tissue which allows the corn to glide freely over the 
underlying structures. We find excellent examples of corns in the 
ischial callosities of the Cynomorpha and in the callous pads found 
on the feet of Carnivora. 
The right funicular pouch of peritoneum of Macacus sinicus, occupied by a 
plug of omentum, 0; the testis, 7. 
Of late years the attention of surgeons has been directed to corns, 
in consequence of a very remarkable affection to which they are 
able. Under certain abnormal conditions of the spinal cord and 
peripheral nerves, such as locomotor ataxy, sclerosis, and peripheral 
neuritis, the corus ulcerate, and at last the ulceration perforates not 
merely the corn, but the whole thickness of the foot; hence it is now 
familiar as the “ perforating ulcer.” 
It was to me a matter of no small interest to find the callous pad 
on the foot of a Civet Cat the seat of a perforating ulcer; the 
interest was considerably heightened when, on opening the spinal 
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