The soft structures are cut at the level of the radio-carpal
articulation, exposing the proximal row of carpal bones. _Cr_,
Radial carpal bone; _Ci_, intermediate carpal bone; _Cu_, ulnar
carpal bone; _Ca_, accessory carpal bone. (After Schmaltz, Atlas d.
Anat. d. Pferdes.)
]
3. The =common interosseous artery= (A. interossea communis) is a vessel
of considerable size which arises at the level of the interosseous
space, through which it passes. Before entering the space it gives off a
small branch, the volar interosseous (A. interossea volaris), which
descends to the radial head of the perforans. In the space it supplies
the nutrient arteries of the radius and ulna. Emerging from the space it
gives off branches to the flexor carpi externus, a small =recurrent
branch= (A. interossea recurrens) which passes upward on the outer
surface of the ulna and anastomoses with the deep brachial and ulnar
arteries, and is continued as the =dorsal interosseous artery=. This
vessel (A. interossea dorsalis) passes down between the anterior and
lateral extensors of the digit and concurs with the anterior radial in
forming a network on the anterior surface of the carpus, the =rete carpi
dorsale=. From the latter arise two small vessels, the =internal= and
=external dorsal metacarpal arteries= (A. metacarpea dorsalis medialis,
lateralis), which run distally in the grooves between the large and
small metacarpal bones and anastomose with the volar metacarpal
arteries.
4. The =artery of the rete carpi volare= (A. retis carpi volaris) is a
small vessel which arises at the distal third of the forearm and passes
downward to the posterior surface of the carpus, where it concurs with
branches of the volar metacarpal arteries in forming the rete carpi
volare.
5. The =external volar metacarpal artery= (A. metacarpea volaris
lateralis) is a small vessel which arises just above the carpus under
cover of the flexor carpi medius and anastomoses with the ulnar artery,
forming the supracarpal arch. From the latter a branch descends with the
outer branch of the median nerve, inclines outward toward the posterior
border of the accessory carpal bone, and arrives at the head of the
external metacarpal bone. Here it is connected with the internal volar
metacarpal artery, usually by two transverse branches, thus forming the
=deep volar= or =subcarpal arch= (Arcus volaris profundus). One of these
branches lies between the subcarpal check ligament and the suspensory
ligament; the other (not always present) lies beneath the latter on the
large metacarpal bone. A small branch descends to the fetlock with the
external metacarpal nerve. Below the arch the artery pursues a flexuous
course downward on the posterior face of the large metacarpal bone
alongside of the external small metacarpal and under cover of the
suspensory ligament. At the distal third of the metacarpus it commonly
unites with the corresponding vessel of the inner side to form a short
trunk which passes backward through the angle of divergence of the
branches of the suspensory ligament and joins the external digital or
the common digital artery.
[Illustration: