PLANTAR SYSTEM. 419 



Of the External Parts. 



The Hoof. 



The hoof is the horny case or covering Nature has provided 

 for the protection of the sensitive parts of the foot. It may be 

 said of itself to constitute such a shoe or defence, as enables 

 the animal in his wild state to travel about in quest of food, not 

 only without injury to the structures underneath it, but with a 

 degree of elasticity that preserves his whole frame from concus- 

 sion. Were one forced into any comparison of the sort, it rnust 

 be admitted that the hoofs of animals bear some anatomical 

 affinity to the human nails, or claws of other animals ; though 

 they are vastly superior in physiological importance to any such 

 appendages as these. 



Form. — Sainbel viewed the foot as " the segment of an oval, 

 opened at the back, and nearly round in front." To a common 

 observer, the hoof exhibits a conoid form ; the part resting upon 

 the ground being the basis ; the vacuity above, the obtruncated 

 apex. Mr. Bracy Clark asserts that this view is incorrect, and 

 that the general figure of the hoof is a cylinder, very obliquely 

 truncated upon its ground surface. This he demonstrates in two 

 ways ; either by rolling up a piece of paper into the shape of a 

 cylinder, and afterwards cutting one of its ends in a very slanting 

 direction ; or by taking a carpenter's square, and placing one 

 limb beneath the foot across the quarters, then sloping the other 

 backward against the side of the quarters, parallel to the front, 

 when the edge of the iron will be found parallel to the wall of 

 the hoof. This corrected view of its figure will serve to account 

 for the general equiformity manifest in the hoof, and also for the 

 undeviating correspondence found to exist between its slope or 

 slant, as well in front as behind, which in an ordinary or healthy 

 foot may be estimated at an angle of 45°. Around the coronet, 

 where the hoof unites with the skin, the cylinder is cut directly 

 across its perpendicular — at right angles with it : it is the oblique 

 truncation of its ground-surface that occasions the slant, which 

 latter we may consequently increase at pleasure by any means 

 that augment the former, viz. by lowering the heels ; by cutting 

 away a prominent frog ; or by putting on thin-heeled shoes. At 

 the same time that we increase the slant of the hoof, we increase 

 the obliquity of the pasterns, and likewise proportionately aug- 

 ment the ground-surface of the hoof, from heel to toe, the breadth 

 remahiing unaltered ; and in the same ratio, consequently, ex- 

 tend the surface of tread*. 



* For further elucidation on the cylindrical form of the foot, consult 

 Mr. Bracy Clark's worlvs on the Foot of the Horse. 



