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A MANUAL OF VETERINARY PHYSIOLOGY 



WHITE LIME 



each other, and confer on the part its fibrous character and elasticity. 

 The horn of the pad contains much more moisture than that of any- 

 other part of the foot, and it is the moisture which confers on it 

 its peculiar soft pliable condition, aided by the secretion of the sweat 

 glands of the plantar cushion. The foot-pad grows from the vascular 

 membrane covering the plantar cushion. The overgrowth of horn 

 is provided against by a method which is a combination of that 

 found in the wall and sole — viz., it is cast off after growing to a certain 

 thickness, while the part next the ground is worn away by friction. 



In consequence, owing 

 to its rubber-like nature, 

 rags of horn along the 

 edges of the foot-pad 

 are a common and 

 natural condition. 



A transverse section 

 of the foot-pad at its 

 posterior part resembles 

 in appearance the letter 

 W. The two lower 

 points are the sides of 

 the pad ; the space be- 

 tween them is the so- 

 called 'cleft,' or central 

 depression (see Fig. 233, 

 j). Above the cleft on 

 that side of the pad 

 next to the sensitive 

 foot is a projection of 

 horn known as the 

 ' frog-stay,' or ■ peak.' 

 The function which has 

 been assigned to this 

 peak is to prevent the 

 parts becoming dis- 

 placed ; but its position, 

 shape, and connection 

 suggests that it acts 

 the part of a wedge, 

 being forced upwards 

 under pressure when 

 the foot comes to the 

 ground, and it may thus 

 exert a central pressure 

 on the plantar cushion 

 and assist in the expansion of the foot. But it appears, however, 

 to be more valuable as a means of stimulating the nerve-endings 

 in the plantar cushion, which are especially abundant in this region, 

 and so acting the part of a touch organ. 



The Structure of Horn. — The horn of the foot consists of epithelial 

 cells which have undergone compression and keratinisation, by 

 which latter process they become hard and tough. It is possible 

 to have horn in the foot which is not keratinised, and the two are 

 very readily distinguished by the process of staining. The double 

 stain picro-carmine has a selective affinity for each kind of horny 

 tissue ; the carmine picks out the protoplasmic and non-corneous 



Fig. 232. — The Junction of the Horn Tissues 

 of the Wall and Sole. 



A. Diagram of the wall, horn laminae, and sole. 

 Between each horn lamina may be seen the fora- 

 mina, into which the papillae on the terminal 

 end of the vascular laminae fit. Note the rounded 

 termination of the horn laminae. 



B. Microscopical appearance of a horizontal section 

 of the junction of wall and sole ; the horn laminae 

 are wavy, devoid of secondary laminae, and be- 

 tween each may be seen the papillae in section. 

 On the right of the figure the horn tubes of 

 the sole are shown. 



