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 

 foraminte on its laminal surface. The descending branches, 

 larger in size, also penetrate the substance of the pedal 

 bone, and emerge in turn from the foraminae cribbling its 

 outer surface — in this case the set of larger foramina 

 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 Circuni- 

 Jiex Artery of the Toe. 



E. THE VEINS. 



These commence at the foot with a series of plexuses, 

 which may be described as forming (1) x\n Inteknal or 

 Intra-osseous Venous System, and (2) An External or 

 Extra-osseous Venous System. 



1. The Intra-osseous Venous System. — 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 foraminae, 

 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. The Extra-osseous 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. 



(h) The Podojihyllous Plexus. 



(e) The Coronary Plexus. 



