3. The =superior collateral ulnar artery= is often double, and does not
extend to the carpus.
The =median artery= (posterior radial artery) descends along the inner
part of the posterior surface of the radius and divides near the middle
of the forearm into the radial and ulnar arteries. It gives off at the
upper third of the forearm the =common interosseous artery=, a large
vessel which anastomoses with the deep brachial, passes through the
proximal interosseous space, and descends (as the dorsal interosseous)
in the groove between the radius and ulna, and concurs in the formation
of the rete carpi dorsale. At the distal end of the forearm it sends a
branch through the distal interosseous space, which passes downward,
assists in forming the rete carpi volare, and is continued in the
metacarpus as the external deep volar metacarpal artery. This is a small
vessel which passes down under the outer border of the suspensory
ligament and assists in forming the deep volar arch near the fetlock.
[Illustration:
FIG. 470.—ARTERIES OF DISTAL PART OF RIGHT FORE LIMB OF OX, ANTERIOR
VIEW.
_a_, Interosseous artery; _b_, dorsal branch of radial artery; _c_,
rete carpi dorsale; _d_, dorsal metacarpal artery; _e_, dorsal
common digital artery; _f_, _f_, dorsal proper digital arteries.
]
[Illustration:
FIG. 471.—ARTERIES OF DISTAL PART OF RIGHT FORE LIMB OF OX, POSTERIOR
VIEW.
_g_, Ulnar artery; _h_, radial artery; _i_, volar branch of common
interosseous artery; _k_, _l_, _m_, deep volar metacarpal arteries;
_A.v._, volar arches; _n_, volar common digital artery; _o_, _o′_,
_p_, volar proper digital arteries.
]
The =radial artery= is smaller than the ulnar. It descends on the flexor
carpi internus, passes over the postero-internal surface of the carpus,
and is continued as the internal deep volar metacarpal. At the distal
end of the forearm and at the carpus it furnishes branches to the retia
carpi. Another branch (A. met. perforans proximalis) runs outward
between the suspensory ligament and the large metacarpal bone, passes
through the proximal foramen of the bone, and unites with the
interosseous artery; before passing through the foramen it detaches the
middle deep volar metacarpal artery (A. met. volaris prof. III.), which
descends on the posterior face of the metacarpal bone, receives an
anastomotic branch from the internal deep artery, and concurs in the
formation of the deep volar arch above the fetlock.
The =ulnar artery=, the larger of the two divisions of the median,
descends under cover of the flexor carpi internus without giving off any
large branches in the forearm. It passes through the carpal canal and
continues along the inner side of the deep flexor tendon as the =volar
common digital artery=. At the distal third of the metacarpus this
vessel is joined by a branch from the internal deep volar metacarpal
artery, forming the superficial volar arch. Near this another branch of
the common digital (or of the internal digital) passes around the outer
border of the flexor tendons to the posterior face of the metacarpal
bone and concurs with the deep volar metacarpal arteries in the
formation of the deep volar arch. A branch from the arch passes forward
through the inferior foramen of the metacarpal bone and joins the dorsal
metacarpal artery which descends from the rete carpi dorsale in the
anterior metacarpal groove.
The =volar common digital artery= (A. metacarpea volaris superficialis
III.) passes into the interdigital space and divides into two =volar
proper digital arteries=, which descend along the interdigital surfaces
of the chief digits and pass through the foramina at the upper part of
the interdigital surfaces of the third phalanges, enter the cavities in
these bones, and ramify in a manner similar to the corresponding vessels
in the horse. The volar common digital detaches a branch (A.
interdigitalis perforans) which passes forward through the upper part of
the interdigital space and anastomoses with the dorsal metacarpal
artery.
The volar proper digital arteries (or the common digital) give off, in
addition to other collaterals, branches which correspond to the
arteries of the plantar cushion of the horse. These pass to the bulbs
of the claws and anastomose with each other and with the inner and
outer digital arteries, forming an arch from which numerous branches
are distributed to the matrix of the hoofs.
The =dorsal metacarpal artery= (A. met. dorsalis III.) is a small vessel
which arises from the rete carpi dorsale, descends in the groove on the
anterior face of the metacarpal bone, and is joined by the inferior
perforating metacarpal artery from the deep volar arch to constitute the
dorsal common digital artery. This vessel (A. digitalis communis
dorsalis III.) divides into two =dorsal proper digital arteries=.
The =internal digital artery= (A. digiti III. medialis) is the
continuation of the internal deep volar metacarpal artery. It descends
on the inner side of the inner digit and terminates at the bulb of the
claw by anastomosing with the corresponding volar proper digital artery.
It gives off a branch to the rudimentary digit and forms a transverse
anastomosis behind the first phalanx with the volar common digital or
its inner division.
The =external digital artery= (A. digiti IV. lateralis) arises from the
deep volar arch, passes down on the outer side of the external digit and
is distributed like the inner one.