PLANTAR SYSTEM. 439 



sure of coronary substance which but tensely and smoothly 

 covered the latter, admitted of being disposed in gathers or folds 

 so soon as it reached the former. Posteriorly, the coronary sub- 

 stance forms a junction, indeed becomes continuous in substance, 

 with the heels of the sensitive frog. 



Structure. — The coronary substance discloses three different 

 parts in its composition : — 1. A Jibro-cartilaginous circling band, 

 forming the substratum and basis of the entire structure. 2. A 

 cuticular covering, so called from its resemblance in texture to 

 the cutis. 3. A network of bloodvessels, reposing upon the for- 

 mer, and covered by the latter. The cartilaginous structure, 

 freed from its vascular connexions, is found to be wrought in the 

 form of a coarse, open, irregular network, and appears designed 

 mainly for the purpose of affording a bed for the lodgment and 

 ramification of the bloodvessels destined to produce the wall. 

 The looseness of its connexion, added to its own elasticity, ren- 

 ders this substance peculiarly adapted to accommodate itself to the 

 motions of the coffin-joint, and thus preventing those movements 

 from operating prejudicially to the superimposed glandular struc- 

 ture. 



Organization. — The coronary substance may be ranked among 

 the most vascular parts of the body : no gland even possesses, 

 for its magnitude, a greater abundance of bloodvessels, or of 

 bloodvessels (taking them generally) of larger size ; nor does 

 there exist any part in which greater care appears to have been 

 taken to arrange its vessels so as to insure an uninterrupted 

 supply of blood. These vessels it is that produce the wall : and 

 there is every reason to believe that they perform this office 

 without any assistance from the vessels of the laminae. 



The Cartilages 



Are two broad, scabrous, concavo-convex, cartilaginous plates, 

 erected upon the sides and wings of the coffin-bone. Professor 

 Coleman calls them " the lateral cartilages," in contradistinc- 

 tion to two others he has named " the inferior cartilages." 



Situation. — The cartilages form the postero-lateral parts of the 

 sensitive foot, extending the surface considerably in both these 

 directions. 



Attachment. — The cartilages are fixed into fossae excavated in 

 the supero-lateral borders of the coffin-bone. Their anterior 

 parts become united, on each side, with descending lateral ex- 

 pansions from the extensor tendon, and are also attached to the 

 coronet bone by cellular membrane. Their posterior parts sur- 

 mount the al(e or wings of the bone, to which they are firmly 

 fixed, and from which they project backwards, beyond the bone. 



