550 



^ESTHESIOLOGY. 



SENSITIVE STRUCTURES. 



Attached to the inner surface of the hoof is the sensitive 

 portion of the foot, which may, like the hoof itself, be divided 

 into the regions of the wall, the sole, the frog, and the coronary 

 band. The extremity of the digit has been regarded, not inaptly, 

 as being enveloped in a sensitive sheath, which extends upwards 

 beyond the level of the coffin joint, and becomes continuous with 

 the skin. This sheath has been called the keratogenous mem- 

 brane, since on its outer surface it is endowed with the function 

 of secreting horn tissue, for the renewal of the various parts of 

 the hoof. The part of this membrane which forms the coronary 

 band is villous or papillated ; that forming the sensitive wall is 



laminated, constituting what has been 

 termed \h& podophyllous tissue; finally, 

 that forming the sensitive sole and frog 

 is finely villous, and may be called the 

 velvety tissue. 



The SENSITIVE FROG occupies the pos- 

 terior and central parts of the foot, filling 

 up the irregular space between the lateral 

 cartilages, flexor tendon, and os pedis. 

 Bounded laterally by the cartilages, 

 superiorly by the perforans tendon and 

 common integument, infero-externally 

 by the horny frog, it is continuous with 

 the sensitive bars and sole, and the 

 coronary ligament. Like the horny 

 frog, it presents two surfaces, two lateral borders, a base, 

 and an apex. The super o-anterior surface is related with the 

 strengthening sheath of the flexor tendon, the ligament of the 

 navicular joint, and the ala? of the os pedis ; the infero-posterior 

 surface is covered by villi, from which the horny frog is secreted, 

 and in its centre is a deep cavity for the insertion of the frog- 

 stay. The base looks backwards, and is divided into two bulbous 

 enlargements, which are united to the lateral cartilages. The 

 summit looks forwards, and is attached to the plantar surface of 

 the os pedis in front of the semilunar ridge. The lateral surfaces 

 correspond to the commissures of the frog, and are continuous 

 with the inner surface of the lateral cartilages. The sensitive 

 frog is made up of an external layer of cuticular structure, the 



FIG. 214. 



Sensitive foot solar aspect. 

 a, Velvety tissue of the sole ; 6, 

 That of frog. 



