280 OUTLINES or EQUINE ANATOMY. 



very acute angle at the apex. These are separated by the 

 cleft, and on either side laterally blend with the sensitive 

 sole. On the ridges are very marked papillae, which gra- 

 dually decrease in size in extending from the prominences 

 until they are absent at the line of junction with the sole. 

 There is a slight line caused by diminution in size of the 

 papillae, mapping out the boundary of the commissures. It 

 may be noticed that the papillae of the frog are smaller 

 than those of the sole and of the coronary secreting sub- 

 stance. The vascular horn-secreting layer in all parts 

 consists of loose areolar tissue, with very numerous vessels 

 ramifying through it. The vascular sole is connected to 

 iKe bone by loose areolar tissue, in which is situated a 

 plexus of veins, and the solar arteries running from the 

 artery of the frog outwards in a radiating manner to the 

 circumflex artery of the toe, which runs round the outer 

 circumferent margin of the plantar surface of os pedis. 

 The sensitive laminae are connected by denser areolar 

 tissue, which attaches them to the antero -lateral surface 

 of OS pedis, where they cover the lateral laminal arteries 

 and the branches they send upwards to the superficial 

 coronary artery, and downwards to the circumflex artery 

 of the toe. The sensitive layer of the coronary secreting 

 substance is firmly attached to a somewhat dense band of 

 substance (fibrous coronary band) which extends round 

 the coronet. This is deepest at the toe, where it is attached 

 to extensor pedis tendon at its insertion ; laterally it rests 

 on the centre of the lateral cartilage (external surface), 

 and posteriorly it terminates in blending with the fibrous 

 or fatty frog. This is an elastic substance, occupying the 

 centre of the posterior part of the foot. It consists of a 

 quantity of yellow elastic tissue arranged in fibres, which 

 interlace in all directions, but the largest of which take a 

 direction obliquely from above downwards and forwards. 

 In the meshes of these fibres is a quantity of substance 

 apparently of a fatty nature, whence this organ has 

 received the name of fatty frog. It is a wedge-shaped 

 body with two surfaces, a base and an apex. The S2iperior 

 surface lies in contact with the under surface of the ex- 

 panded perforans tendon, with the intervention of a thin 

 fibrous layer. It extends forwards on co the plantar sur- 

 face of OS pedis at the posterior crescentic margin at its 

 centre, where it forms a triangular projection. Its hase 



