440 PLANTAR SYSTEM. 



giving form and substance to the heel. Supposing one of the car 

 tilages to be divided into two equal parts by a line drawn horizon- 

 tally across its middle, the superior half, which extends as high as 

 the pastern-joint, is covered by skin only ; and on that account 

 is quite perceptible to the feel, and (in form) to the sight, as the 

 animal stands with his side towards us. The lower half is covered, 

 superiorly, by the encircling coronary substance ; inferiorly, by 

 sensitive laminae : consequently, over all by the hoof, wiiich 

 envelopes both the coronary substance and the laminae. The 

 extreme posterior ends of the cartilages incurvate downward and 

 backward ; but, being overreached by the heels of the sensitive 

 frog, any abrupt or exposed termination of them is prevented. 

 Around these points also the coronary substance makes its in- 

 flections upon the sensitive frog, thereby giving them additional 

 substance and support. 



Form. — Considered in the detached state, the cartilage in its 

 general figure describes an irregular quadrangle, of which the 

 supero-anterior and infero-posterior angles are the most project- 

 ing ; the latter at the same time being incurvated inwards. Ex- 

 ternally, the cartilage is pretty regularly convex ; internally, it 

 is unevenly concave, the surrounding border turning inwards 

 into the substance of the sensitive frog. The posterior part of 

 the cartilage is somewhat thinner than the anterior, and has 

 several foramina through it — three or four of large size — which 

 transmit vessels to the frog. 



THE FALSE CARTILAGES.— From the inferior and pos- 

 terior sides of the true cartilages, proceed in a direction forward — 

 towards the heels of the coffin-bone — two fibro-cartilaginous 

 productions, to which Mr. Coleman has given the name of" in- 

 Jerior cartilages." If they are to be considered as t«////oofsatall, 

 I prefer denominating themy"a/se ; they being, as well in structure 

 as in use, different from the true or lateral cartilages. They 

 spread inwards upon the surface of the tendo perforans ; become 

 united at their inner sides with the superior margin of the sensi- 

 tive frog ; are covered inferiorly by the sensitive sole; and at the 

 same time assist in the support of the sensitive frog. They are 

 triangular in their figure, and are arched in the same manner as 

 the sole. 



Use. — Their use appears to me to be, to fill up the triangular 

 vacant spaces left between the tendo perforans and heels of the 

 coffin-bone, thereby completing the surface of support for the 

 sensitive frog, and extending that for the expansion of the sensi- 

 tive sole. Bone in these places must have proved inconvenient 

 by more or less impeding the impression upon — and consequent 

 reaction of — the sensitive frog. 



