Page 66 - Adams and Stashak's Lameness in Horses, 7th Edition

32 Chapter 1

Nerves and Vessels The nutrient artery of the humerus may come from the
first part of the collateral ulnar artery, or it may arise
The ventral branches of spinal nerves C6 through T2
VetBooks.ir create the brachial plexus, which perforates the scalenus from the brachial artery.
muscle and passes into the forelimb craniomedial to the
shoulder joint (Figure 1.27). Vessels supplying the tho­
racic limb accompany the nerves in this location. Lymphatic Drainage
Lymphatic vessels from structures distal to the elbow
Suprascapular vessels accompany the suprascapular
nerve, passing laterad between the subscapular and are afferent to the cubital lymph nodes, a group of 5–20
small nodes found just proximal to the medial side of
suprascapular muscles. The median nerve descends with
the axillary artery, forming a loop medial to the artery the elbow (Figure 1.27). Efferent vessels from the cubital
lymph nodes end in the proper axillary lymph nodes on
by uniting with a large branch from the musculocutane­
ous nerve. Proximal branches from the musculocutane­ the medial surface of the teres major muscle (Figure 1.27).
These also receive lymph from the muscles of the arm
ous nerve supply the coracobrachialis and biceps brachii
muscles. Distal to the axillary loop, the median and and shoulder and from the adjacent skin and the ventro­
lateral trunk. Vessels from the proper axillary lymph
musculocutaneous nerves are contained in a common
sheath, coursing distad along with the brachial artery. In nodes carry lymph to the caudal deep cervical lymph
nodes. Some efferents of the deep cervical nodes drain
the middle of the arm, the musculocutaneous nerve ter­
minates by dividing into a distal branch supplying the directly into the venous system; others pass to other
regional nodes and therefore drain indirectly through
brachialis muscle and the medial cutaneous antebrachial 28
nerve that spirals around the biceps brachii to the lacer­ these to the venous system.
Lymphatic vessels from the skin of the entire thoracic
tus fibrosus.
The axillary nerve crosses the medial surface of the limb, neck, and dorsolateral trunk and more proximal
subscapularis muscle, and, together with the large sub­ parts of the limb are afferent to the superficial cervical
scapular vessels (from the axillary vessels), the nerve lymphocenter on the cranial border of the subclavius
muscle, deep to the brachiocephalicus. Efferent lym­
passes laterad between the subscapularis and teres major
muscles. Innervating these muscles and others of the phatic vessels from the superficial cervical lymph nodes
terminate in the caudal deep cervical lymph nodes or by
caudal shoulder, the axillary nerve is accompanied by 16,28
the caudal circumflex humeral artery, a branch of the entering the common jugular vein.
subscapular artery. It ultimately gives rise to the cranial
cutaneous antebrachial nerve. Stay Apparatus of the Thoracic Limb
The large radial nerve and smaller ulnar nerve
descend close to each other medial to the subscapular Muscles, tendons, and ligaments constituting the stay
artery and then caudal to the brachial vein. After supply­ apparatus of the thoracic limb fix the carpus, elbow, and
ing a branch to the tensor fasciae antebrachii muscle, the shoulder joints in the standing position (Figure 1.32).
radial nerve plunges laterad between the teres major and This complex of structures functions almost entirely as
the triceps to run along the musculospiral groove of the a passive, force‐resisting system. It permits the horse to
35
humerus. Here it gives off lateral cutaneous branches to stand (and sleep) with a minimum of muscular activity.
the caudodistal aspect of the arm and supplies branches The elasticity of the tissues in the stay apparatus also
to the triceps brachii and anconeus muscles. Just proxi­ stores energy during weight‐bearing and redeliver that
mal to the elbow joint, the radial nerve divides into deep energy back to the limb during the swing phase of gait,
and superficial branches. The deep branch supplies the markedly improving the efficiency of movement, espe­
craniolateral muscles of the antebrachium. The superfi­ cially when working at speed.
cial branch winds laterad between the lateral head of the In the manus, elements of the stay apparatus resist
triceps brachii and the extensor carpi radialis muscles nonphysiologic hyperextension of the fetlock and inter­
accompanied by the transverse cubital artery. It gives phalangeal joints.
rise to the lateral cutaneous antebrachial nerve, which The DDFT forms a continuous ligamentous band
supplies sensory innervation to the fascia and skin of the from its accessory (carpal check) ligament to the solar
lateral aspect of the forearm (Figure 1.30). surface of the distal phalanx. This is the only element
The ulnar nerve angles caudodistad to the middle of that resists hyperextension of the distal interphalangeal
the arm. It gives rise to the caudal cutaneous antebra­ joint; as a consequence, disruption of this part of the
chial nerve that courses across the medial surface of the suspensory apparatus can produce a characteristic
tensor fasciae antebrachii (Figure 1.27). The continua­ hyperextension of the coffin joint, identifiable as the
tion of the ulnar nerve passes between that muscle and foot is rotated back onto the heels and the toe lifts from
the medial head of the triceps brachii, accompanied here the ground.
by the collateral ulnar vessels as they cross the medial The four palmar ligaments stretched tightly across
humeral epicondyle. the pastern joint, the straight distal sesamoidean liga­
After giving off the cranial circumflex humeral ves­ ment, and the digital flexor tendons (with their acces­
sels in the proximal part of the brachium, the axillary sory ligaments) prevent hyperextension of the pastern
vessels continue as the brachial artery and vein. As they joint.
descend the arm they give rise to the deep brachial ves­ The suspensory apparatus is a ligamentous contin­
sels supplying the triceps muscle and then the collateral uum extending from the proximal end of the third meta­
ulnar vessels caudally and the bicipital vessels cranially. carpal bone to the proximal and middle phalanges. It
The transverse cubital vessels are given off cranially consists of the suspensory ligament, palmar ligament
and pass distolaterad deep to the biceps brachii and bra­ with its embedded proximal sesamoid bones, and the
chialis muscles to the cranial aspect of the cubital joint. distal sesamoidean ligaments. The SDFTs and DDFTs