912 



TEE SENSORY APPARATUSES. 



The surface of the organ shows filiform prolongations, a little constricted at 

 their base, and named papiJlcE, viUo-papiUcB, villi, and villous loops, the size of 

 which is greatest towards the lower part of the cushion ; those of the perioplic 

 ring are smallest. Contained within the minute apertures at the upper part 

 of the hoof -wall, these papillaB— considered as a whole, and when the hoof has 

 been removed by maceration — form a tufty surface most perfectly seen when the 

 foot is suspended in water. 



The structure of the coronary cushion resembles that of the derma, of which 

 it is in reality only a continuation. It comprises a fibrous framework, remark- 

 able for its thickness and density, with a considerable number of vessels and 

 nerves, the ramifications of which may be followed to the extremity of the villi. 



Fig. 493. 



LATERAL VIEW OF THE HORSE'S FOOT, 

 AFTER REMOVAL OF THE HOOF. 



1, Perioplic ring, divided by a narrow 

 groove from the coronary cushion, 

 2, which is continuous with the 

 plantar cushion, 4, and join= the 

 vasculnr laminae, 3, through the 

 medium of the white zone. 



HIGHLY MAGNIFIED HORIZONTAL SECTION OF A HORSE'S 

 HOOF, SHOWING THE RELATIONS BETWEEN A KERA- 

 PHYLLOUS AND A PODOPHYLLOUS LAMINA. 



1, Principal podophyllous lamina; 2, secondary ditto 

 {laminella) \ 3, elliptical cells (analogous to the generat- 

 ing layer in the rete Malphigii) ; 4. cells of the same, 

 but already keratinized, and colourable by carmine ; 5, 

 ke)ai>hyllous lamina. 



To its great vascularity is due the bright red colour it shows on its surface ; 

 this colour is sometimes masked by black pigment. 



(I have found a notable quantity of adipose tissue in the cushion). 



2. Velvety Tissue. — Much thinner than the plantar cushion, the velvety 

 tissue— the formative organ of the sole and frog — extends over the whole of the 

 plantar region of the third phalanx, as well as the plantar cushion, the bulbs of 

 which, and the pyramidal prominence it covers, by adapting itself exactly to the 

 irregularities of this elastic mass. 



Its surface, which altogether resembles the general configuration of the 

 plantar surface of the hoof, is divisible into two regions — a central, correspond- 

 ing to the pyramidal body and the frog, and continuous on the bulbs of the 

 cushion with the extremities of the coronary cushion and the perioplic ring, but 

 chiefly with the latter ; the other, peripheral, is covered by the horny sole. 



