812 THE APPARATUS OF THE SENSES. 



states, these cells are formed in planes parallel with the surface that 

 secretes them ; consequently, around the papillae they are more or less 

 vertical, while between them they are horizontal. The walls of the tubes, 

 or fibres, are therefore composed of cells disposed in a vertical manner; 

 while in the interfibrous horny matter they are arranged in the opposite 

 direction. The loose nodulated contents of the tubes is composed of cells 

 thrown off from the termination of the papilla, and corresponds to the pith 

 of feathers. The soft cells interposed between the vascular and horny 

 laminae are carried down to the lower margin of the wall, where, with the 

 elastic horn secreted by the papillae which terminate the former, they 

 constitute the peculiar light-coloured band, or " white line," which marks 

 the junction of the sole with the wall (Fig. 379). This intermediate band 

 of soft flexible horn at this point obviates tearing of the sole from the wall, 

 and fracture of the former. The cells of the horny laminae are more or less 

 fusiform. 



M. Chauveau has also evidently overlooked the presence of beautiful 

 lateral leaflets on the sides of the horny laminae, corresponding to those on 

 the vascular leaves. These were observed by me in 1858; in 1862 they 

 were described by Rawitsch and Ercolani, and, at a later period, by Colin of 

 Alfort and Leisering of Dresden. They are very conspicuous in a well- 

 prepared section (Fig. 380, d"). 



It should be observed that the growth of the wall of the hoof is 

 indefinite, but that the sole and frog, after attaining a certain thickness, 

 exfoliate. For complete details as to the physiology of the Horse's foot, the 

 student is referred to the c Veterinarian' for 1871.) 



2. The Claws of Ruminants and Pachyderms. 



In the Ox, Sheep, and Pig, the plantar cushion covers the bulb of the heel of each 

 digit, where it forms a convex mass ; it extends to the insertion of the deep flexor 

 tendons of the phalanges, in becoming triangular in shape, and thinner. The horny 

 envelope covering the extremity of the digits of these animals is a kind of cupola, 

 having almost the form of the third phalanx ; it is usually named the claw. 



The claw of the Ox has an outer face resembling the wall of the Horse's hoof, and an 

 inner face which is slightly concave, and marked by undulating grooves ; owing to this 

 concavity, the two claws of each foot only touch at the extremities of their adjacent 

 faces. The plantar region of the claw is slightly depressed, and but little developed ; 

 it is chiefly made up of the plantar cushion, which is covered by a thin layer of supple 

 tubular horn. On the interior of Ihe claw is seen a wide shallow cutigeral cavity, 

 perforated by very fine openings, and laminae thinner and more numerous than in the 

 Horse's hoof. The tubes of the claw-horn are very small, being surpassed in diameter by 

 those of the periople and sole. 



Above and behind each claw are two little rudimentary horny capsules, which are 

 named ergots. (Each contains a small bone, which is not attached to the skeleton in 

 Kuminants. In the Pig, these rudimentary claws are larger, and are connected with the 

 bones of the leg. In this animal the horn of the claws is altogether thinner, softer, 

 and less resisting than in Soliperls. The ergot is the representative of those digits which 

 are apparently absent in the solid and cloven foot.) 



3. The Claws of Carnwora. 



In these animals, the third phalanx of the digits is enveloped in a conical horny 

 sheath that curves downwards like the bone itself. This covering is designated the 

 claw or nail, and offers somewhat the same organisation as the horns of Kuminants ; it 

 is developed, and grows in the same manner, as the hoof of Solipeds, its matrix being a 

 prolongation of the corium which extends over the third phalanx, after dipping into 

 the circular furrow at the base of that bone. 



_ Placed at the extremity of the digital region, the claw in these animals is not 

 utilised hi locomotion, as the foot does not rest on the ground by the extremities of the 



