PLANTAR SYSTEM. 433 



ordinary state of the hoof altogether imperceptible. For drawing 

 our attention to this part we are indebted to Mr. Clark ; and 

 insomuch as he considers it to be a production of the cutis (not 

 having any connexion with the glandular circle that secretes 

 the wall), and to serve the purpose of " uniting the sensible 

 parts with the insensible," I agree with him. I find something 

 very similar to this growing upon the human nail, issuing fron^ 

 the superior edge of the terminating border of the cutis, and 

 continued from the cuticle, which proceeds for some way upon 

 the nail, uniting it more closely and firmly with the cutis, and 

 protecting the latter from external injury. This production is no 

 more the beginning of the nail itself than is the so-called y/oo- 

 band the commencement of the wall : they are both distinct 

 parts, though but supplementary ones, and seem to be of a 

 nature j^artaking both of horn and cuticle. It has no more im- 

 portant relation to the frog, in my opinion, than it has to the 

 wall : it serves the same purpose to both, — that of strapping up the 

 heels of the frog and binding them in closer and more intimate 

 connexion with the neighbouring parts. Were I asked what other 

 use it appeared to have, I should say, that it was formed to cover 

 and protect fro)a hijury the new-formed horn of the hoof, guarding 

 it in its passage downward, until it has acquired substance and 

 hardness sufficient to resist external impressions of itself. 



Development of the Hoof. 



During the early months of fcetality, no horn or hoof is to be 

 found. The foot is covered with a substance, white, firm, and 

 elastic, resembling cartilage in its appearance, but proving more 

 of the nature of cuticle on examination, which supplies the place 

 of hoof. At the coronet this substance takes its origin from the 

 cutis, being found to be continuous with the cuticle ; but that 

 which covers the bottom of the foot is a production from tlie sen- 

 sitive sole and frog. Altogether, it possesses the general form 

 and appearance of the hoof, differing however in these particu- 

 lars — that the substitute for the wall is comparatively thin in 

 its substance ; while that which grows from the bottom of the 

 foot is enormously thick, and, instead of being shaped into sole 

 and frog, exuberates to a degree to constitute club-footedness. 

 About the same period at which the pastern and coffin-bones 

 take on ossification, horn makes its appearance underneath this 

 cuticular wall, in the form of plates descending from the coronet, 

 exhibiting with peculiar distinctness the lamellated structure. 

 The horny wall becomes considerably advanced before we per- 

 ceive any change in the bottom of the foot. At length, horn is 

 detected forming underneath the cuticular substance, vvhich, 

 3 K 



