68o 



A MANUAL OF VETERINARY PHYSIOLOGY 



backwards and downwards (Fig. 241, A). In all fast paces, 

 when the foot comes to the ground, the posterior wall and foot- 

 pad first receive the weight. Under the influence of the body 

 weight the foot-pad, as we have seen, is compressed and becomes 

 wider ; the plantar cushion with which it is closely in contact is 

 also compressed and becomes wider. The effect of this increase 

 in width is that the foot-pad presses on the bars, while the plantar 

 cushion presses on the cartilages, both of which, yielding laterally, 

 force apart the wall at the heels (Figs. 240 and 241, B). When 



the weight is taken off the foot 

 the heels return to their original 

 position, and the foot becomes 

 narrower. The increase in width 

 which the foot undergoes is some- 

 thing very small ; this is probably 

 the reason why for years its exist- 

 ence has been disputed, especially 

 in this country.* The employ- 

 ment of delicate apparatus such as 

 that used by Lungwitzf and the 

 writer]: (Fig. 242), and experi- 

 ments upon feet which have not 

 been mutilated in shoeing, have 

 placed the question beyond all 

 doubt. 



The area over which the wall 

 expands can be seen in Fig. 

 241, A ; the shaded portion of the 

 dotted outline shows the portion heel represents the part which 

 of the foot which has yielded yj elds laterally." At times ex- 



laterally under the influence of J J , . , , 



the body weight. pansion can be registered at 



the coronet, and little or none 



on the ground surface ; but as a rule the amount obtained at 



the coronet can also be obtained near the ground. As to 



the amount of expansion no definite statement can be made : 



it is small and is influenced by the shape of the foot ; horses 



with low heels and full, well-developed foot-pads register a 



* Nevertheless, Bracy Clark demonstrated it over one hundred years 

 ago. He says : ' The term " elasticity," however, by its exercise and 

 use will explain, like the principles of gravitation in the hands of the 

 astronomer, nearly everything that before was dark and obscure in the 

 arts of the foot.' W. C. Spooner (' Treatise on the Foot and Leg of 

 the Horse ') stated in 1840 that the expansion of the foot was equal 

 to T V of an inch. 



f The Journal of Comparative Pathology and Therapeutics, vol. iv., p. 3. 

 1891. 



X ' The Apparatus Employed in Inquiring into the Physiology of the 

 Horse's Foot,' Veterinary Record, vol. iv., p. 263. 1891. 



Fig. 240. — Diagram to illustrate 

 the Expansion of the Foot 

 (Lungwitz). 



The unbroken outline illustrates the 

 shape of the foot at rest ; the 



