26 DISEASES OF THE HORSE’S FOOT 
From the semilunar anastomosis radiate two main 
groups of arterial branches, an ascending group and a 
descending one. The ascending branches penetrate the 
substance of the os pedis, and emerge by the numerous 
foramine on its laminal surface. The descending branches, 
larger in size, also penetrate the substance of the pedal 
bone, and emerge in turn from the foramine cribbling its 
outer surface—in this case the set of larger foramine 
opening on its inferior edge. Having gained exit from the 
bone, their frequent anastomosis, right and left, with their 
fellows forms a large vessel following the contour of the 
inferior edge of the os pedis. This constitutes the Curcwm- 
flex Artery of the Toe. 
E. THE VEINS. 
These commence at the foot with a series of plexuses, 
which may be described as forming (1) An INTERNAL oR 
InrRa-osszous Venous System, and (2) AN EXTERNAL oR 
Exrra-osszous VENous System. 
1. Tue InrRa-osszous Venous Systsm.—This is a venous 
system within the structure of, and occupying the semi- 
lunar sinus of the os pedis. It follows in every respect the 
arrangement of the arteries as before described in the same 
region. Efferent vessels emerge from the plantar foramine, 
follow the plantar fissures, and ascend within the basilar 
processes of the os pedis. Here they lie under shelter of 
the lateral cartilages, and assist in the formation of the 
deep layer of the coronary plexus of the extra-osseous 
system. 
2. Tus Exrra-osssous Venous System.—This may be 
regarded as a close-meshed network enveloping the whole 
of the foot. Although a continuous system, it is best 
described by recognising in it three distinct parts: 
(a) The Solar Plexus. 
(b) The Podophyllous Plexus. 
(c) The Coronary Plexus. 
