The =ulnar nerve= (Figs. 441, 442, 443, 520) arises with the median from
the thoracic components of the brachial plexus. It descends between the
brachial artery and vein, accompanied for a short distance by the radial
nerve. It then crosses the vein and continues behind the latter along
the anterior border of the tensor fasciæ antibrachii and dips under that
muscle near the elbow. Here it is joined by the ulnar vessels and passes
downward and backward over the internal epicondyle of the humerus. In
the forearm it crosses obliquely the deep face of the ulnar head of the
flexor carpi medius and descends under the deep fascia with the vessels,
at first on the ulnar head of the perforans, and then between the middle
and external flexors of the carpus. Near the level of the accessory
carpal bone it divides into two terminal branches, superficial and deep.
It gives off two principal collateral branches. The =cutaneous branch=
(Ramus cutaneus palmaris) is detached just before the nerve passes under
the tensor fasciæ antibrachii; it runs downward and backward on that
muscle under cover of the posterior superficial pectoral, becomes
superficial below the elbow and ramifies on the posterior surface and
both sides of the forearm. The =muscular branch= is given off at the
elbow joint and divides to supply the flexors of the digit and the
middle flexor of the carpus. Of the two terminals, the =superficial
branch= (Ramus superficialis) emerges between the tendons of insertion
of the external and middle flexors of the carpus and ramifies on the
dorso-lateral aspect of the carpus and metacarpus. The =deep branch=
(Ramus profundus), after a very short course, unites under cover of the
tendon of the flexor carpi medius with the outer branch of the median
nerve to form the external metacarpal or volar nerve.
[Illustration:
FIG. 521.—CROSS-SECTION OF FOREARM OF HORSE ABOUT THREE INCHES (CA. 8
CM.) BELOW THE ELBOW JOINT.
The deep fascia is designated by red line. _N_, _A_, _V_, Interosseous
vessels and nerve.
]