THE VEINS 209 



The Internal Metatarsal Vein. — This is the largest of the veins of 

 the metatarsal region. It leaves the venous arch referred to and 

 ascends the inner aspect of the limb on the edge of the perforans tendon. 

 Behind the vein is the internal plantar nerve, and between these two 

 structures is the internal unnamed artery which descends from the 

 tarsal arch. When it reaches the upper third of the metatarsus it 

 inclines forwards and upwards, crossing the inner small metatarsal bone 

 and also the large metatarsal ; upon the latter there is frequently 

 present a faint groove indicating the course taken by the vein. It now 

 passes obliquely over the seat of spavin being crossed by the cutaneous 

 branch of the posterior tibial nerve, whilst the vein runs over the 

 cunean division of the tendon of the flexor metatarsi muscle. It runs 

 up the inner aspect of the leg as the anterior root of the internal 

 saphena vein, and is joined by the posterior root on reaching the upper 

 third of the inner aspect of the tibia. 



The course of this vein is very apparent in the living animal, where 

 it crosses the seat of spavin. Its position should be noted when pyro- 

 puncturing an exostosis in this region, and also when performing the 

 operation of cunean tenotomy. When the vessel is abnormally dis- 

 tended it gives rise to the condition commonly known as blood spavin. 

 The vessel may be raised prominently owing to the pressure upon it 

 of some enlargement, such as an exostosis, or the synovial capsule of 

 the joint in cases of bog spavin. 



The External Metatarsal Vein. — From the venous arch near the 

 fetlock this vein runs up the outer aspect of the limb on the edge of 

 the perforans tendon. The external plantar nerve and the external 

 unnamed artery occupy similar relationships to this vein, as do the 

 corresponding structures on the inner aspect of the limb to the internal 

 metatarsal vein. Near the upper end of the metatarsal region it com- 

 municates with the deep metatarsal vein, and it then passes upwards 

 through the tarsal sheath. It runs obliquely upwards and inwards, 

 and w^hen it leaves the sheath above the hock it is found on the inner 



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