Download caudal cutaneous antebrachial nerve

Surface anatomy of the back, shoulder, and arm.
Fig. 1. The horse’s skeleton in left lateral view. Palpable bony prominences at the
shoulder and arm (brachium) are labeled. The sternum is colored yellow so that the
superimposition of bones is clearer. The original figure was drawn by Professor Paul
Martin; Lehrbuch Anatomie der Haustiere, II. Band, 1. Halfte; 1914, Schickhardt und
Ebner, Stuttgart. It has been cropped and, otherwise, modified only slightly.
summit of T4 spinous process
tuber of spine of scapula
manubrium, sternum
deltoid tuberosity
of humerus
olecranon
of the ulna
position of lateral collateral
ligament of elbow joint
Fig. 2. Horse is an Akhal-Teke. Photograph
(cropped to the area considered here) is from
Horse Illustrated, July, 2012. Original
uncropped photo is by Katya Druz;
www.ARND.NL. Palpable prominences of
Fig. 1 are marked by arrows.
Fig. 3. Drawn by David Stewart Geary at the
Western College of Veterinary Medicine
(WCVM) of the University of Saskatchewan.
trapezius,
cervical part
thoracic part
omotransversarius
latissimus dorsi
sternocephalicus
triceps brachii,
long head,
lateral head
brachiocephalicus
superficial
pectoral
deltoideus
deep fascia
Palpable superficial muscles:
The brachiocephalicus and omotransversarius muscles extend the length of the neck.
They lie parallel, beside one another, and are closely united at their apposed borders.
Where they pass superficial to the omohyoideus muscle (they cover it and it cannot
be seen in the above dissection), they are also very closely joined to it. In the donkey,
different from the horse, the omohyoideus becomes much wider where it is deep to
the omotransversarius and brachiocephalicus.
The brachiocephalicus and omotransversarius have distinct attachments: The
brachiocephalicus is the more ventral muscle. From its tendinous intersection, a
vestige of the clavicle in front of the shoulder, the cleidomastoid part of this muscle
passes to the mastoid process of the temporal bone of the skull; and a thin
aponeurosis, a cleidooccipital part, passes from its dorsal border to the nuchal crest.
The cleidobrachialis part passes from the clavicular intersection to attach distally to
the deltoid tuberosity and crest of the humerus. Different from the brachiocephalicus,
the omotransversarius arises not from the skull but from the margin of the wing of the
atlas and the transverse processes of the following two or three vertebrae. It is quite
narrow at its atlantal attachment, and lies beside the dorsal border of the
brachiocephalicus the length of the neck. It expands as it extends caudally, becoming
much wider. It separates from the cleidobrachialis part at that muscle’s attachment to
the humeral crest and continues caudally, attaching to the deep fascia of the lateral
shoulder. These relations are shown in the following figures:
Fig. 4. The omotransversarius, is narrow at its
origin from the wing of the atlas, closely attached to
the dorsal border of the brachiocephalicus the
length of the neck, and expands caudally at its
attachment to the lateral fascia of the shoulder.
Brachiocephalicus, its
cleidomastoideus part and
a thin cleidooccipitalis
aponeurosis (not clearly
shown here) attach to the
mastoid process and
nuchal crest; its
cleidobrachialis part
attaches to the humeral
crest. Yellow arrow
indicates the caudal, thick,
part of the m. cutaneus
colli; see discussion below.
The original figure, above, by Hermann Dittrich, is in Handbuch der Vergleichenden
Anatomie der Haustiere, W. Ellenberger and H. Baum; rev. O. Zietzschmann, E.
Ackerknecht, and H. Grau, 1943, Springer Verlag, Berlin. It is redrawn here, and
modified slightly, in this drawing by David Stewart Geary.
Fig. 5. The insertion of the brachiocephalicus and omotransversarius muscles at the
shoulder and arm is shown in the drawing below, which is also by David Stewart
Geary:
m. cutaneous colli cut away in
part here where, as a thin slip, it
covers the external jugular vein
and, as a thicker bundle (cut
away and not shown here, but
indicated by a yellow arrow in
the figure above), covers the
lowest part of the supf. cerv.
lnn.
external jugular vein
superficial cervical
lymph nodes
m. subclavius
m. omotransversarius
m. brachiocephalicus
Fig. 6. The cutaneous muscles:
m. cutaneus faciei
m. cutaneus colli,
thin part
thick part
m. cutaneus omobrachialis
m. cutaneus trunci
The cutaneous muscles lie within the superficial fascia, deep to the dermis layer of
the skin to which they attach. They move the skin. Three cutaneous muscles are
shown in the shoulder region: m. cutaneus colli, m. cutaneus omobrachialis, and m.
cutaneus trunci. The cutaneus colli has a thick part and a thin part. The thick part is a
more narrow band, at the angle of junction of the neck and shoulder. It is usually
visible under the skin and is palpable. This part arises from the manubrium of the
sternum, passing dorsolaterally across the lower jugular furrow; it is the muscle that,
in bridging the lower part of the jugular furrow, brings about a small depression in
front of its cranial border, the jugular fossa. The thin part continues cranially from the
thick part. It passes forward, covering the jugular furrow, and at the angle of the jaw is
continuous with the m. cutaneus faciei. This part of the cutaneus colli muscle is very
thin. It lies upon the sternomandibularis ventrally, its essentially transverse fibers
extending from the ventral neck dorsally and covering the jugular furrow. This is the
muscle that, in more excitable animals, contracts and erases the jugular furrow on
approach of the veterinarian (and a few other circumstances)!
Fig. 7. The figure below shows only the thin part of the m. cutaneus colli; its fibers,
which would otherwise conceal the jugular furrow, have been removed to expose the
vein. The white dots are placed to show its normal dorsal extent. The location of the
thick part of the cutaneus colli is shown by the solid black lines.
external jugular vein
in the jugular furrow
Thin part of the cutaneus colli; it
lies upon the sternomandibularis
ventrally and is cut away where it
would conceal the ext. jugular vein.
position of jugular fossa
sternomandibularis
arising from manubrium
Position of thick part of
cutaneus colli; it covers the
cephalic vein where it joins
the ext. jugular and the lower
end of the superficial cervical
lymph nodes.
Fig. 8. In this figure, which is from Ellenberger-Baum, all of the cutaneous muscle of
the neck and the trapezius, omotransversarius, brachiocephalicus, deltoideus, and
latissimus dorsi muscles are removed. The attachments-portion of the splenius
muscle, which is to the transverse processes of the cervical vertebrae and the nuchal
crest of the skull, is removed to reveal more clearly the deeper lying muscles. The
omohyoideus is distinguished in that it is closely attached to the omotransversarius
and brachiocephalicus muscles where they pass superficial to it. Both the
omohyodeus and omotransversarius attach caudally to the deep fascia of the
shoulder, the omohyoideus medially, the omotransversarius laterally. The two
muscles pass forward on either side of the scapula, the subclavius muscle and the
superficial cervical lymph nodes. They come together and fuse in front of the lymph
nodes. (Note: A close attachment comes about when there is little loose connective
tissue between the muscles. In this case the muscles are sometimes described as
being “fused.” When the loose connective tissue is abundant, often laden with fat, the
muscles slide easily upon one another.) Functionally, a close attachment probably
means that the muscles act together, in this case, to draw the shoulder forward and
advance the limb. The hyoid attachment of the omohyoideus is complemented by the
strong geniohyoideus muscle, which effectively extends the omohyoid attachment
from the basihyoideum to the more substantial lower jaw.
blue = sternohyoideus position
m.splenius; fleshy part that arises from
funicular ligamentum nuchae and from
the thoracic spines at the withers
to basihyoideum
area of fusion
area in relation to supf. cerv. lnn.
m. subclavius
Fig. 9. Looking at the standing horse from the left side, you see an inverted “V” whose
apex (black arrow) gives the position of the deltoid tuberosity. The line leading down
on the right toward the olecranon in the photograph is the ventral border of the lateral
head of triceps (yellow arrow in the photo). This line always passes just above the
lateral epicondyle of the humerus and the lateral collateral ligament of the elbow joint.
The lateral epicondyle is the proximal attachment of the lateral collateral ligament. A
little in front of the ligament, passing at the lower border of the lateral head, is the
lateral cutaneous antebrachial nerve of the forearm. The nerve is small, but may be
palpable. In any case, its position is clear as the lower border of the lateral head is
always distinct. The nerve is distributed to the skin here but seldom needs to be
blocked. The line leading down to the left (blue arrow in the photograph) indicates the
position of the humeral crest, which is the attachment of the brachiocephalicus and
the descending superficial pectoral. To the right of the crest, in the interval between
the crest and the prominence of the extensor carpi radialis muscle, the skin overlies
the brachialis muscle, which is separated from the skin by superficial fascia and a
thick layer of deep fascia (deep and superficial fasciae are discussed briefly below).
lateral collateral
ligament, elbow joint
Fig. 10. Cutaneous nerves of the thoracic limb, lateral view at the shoulder.
brachialis
extensor carpi radialis
A brief discussion of the skin and fasciae: The skin is made up of a superficial
layer of epithelium, the epidermis, and a deeper layer of dense irregular collagenous
connective tissue, the dermis. The epidermis is a stratified squamous epithelium; it
forms a fairly uniform, thin, layer except on surfaces subject to considerable wear: the
pads of the feet, hoof and claw, lips and muzzle. In these places in our domestic
animals it can be several millimeters thick. Thin or thick, it is often pigmented. The
epidermis lacks vessels and nerves.
Except on areas of the skin subject to wear, the dermis is much thicker than the
epidermis, its thickness depending on whether it covers a relatively protected area of
the body (medial surface of the limbs, ventral surface of the abdomen) or an area
more exposed to the elements. Thus, the dermis layer of the ventral abdomen is
thinner as the abdominal skin is a more protected area but there is a gradual increase
in dermal thickness upon the sides of the body and it is thickest on the back. Different
from the epidermis, the dermis contains small vessels, and sensory and autonomic
nerves. These nerves are small and difficult to discern grossly; but this essential
difference between the dermis, which is innervated, and the epidermis, which is not, is
the basis for techniques of horse-shoeing, nail trimming in small animals, and the like.
Epidermis and dermis constitute the skin or cutis. Beneath the dermis is the
subcutis or subcutaneous tissue; it is what we designate superficial fascia and the
terms may be used interchangeably. The subcutis is a loose connective tissue. It
forms a continuous layer that is uniformly distributed under the skin and joins the skin
to underlying tissues. The subcutis is the superficial fascia, which contains
collagenous, elastic, and reticular fibers, intercellular substance, and bears varying
amounts of fat, which make it possible to slide the skin over the underlying tissues:
deep fascia, muscle and bone. The subcutaneous tissue is scant or absent in those
places (hoof, muzzle of cattle, for example) that allow little or no sliding of the cutis on
the underlying tissues. The large superficial veins and cutaneous nerves that we
observe and palpate in the live animal all occupy the layer of superficial fascia.
Fig. 11. Reflected skin of the ventral abdomen of a donkey.
cutis = skin
epidermis, thin epithelial
layer, often pigmented;
dermis, thicker connective
tissue layer, unpigmented
subcutis = subcutaneous tissue
= superficial fascia
=
The deep fascia is different from the superficial fascia. It is always present as a welldefined sheet or as two or more sheets of collagenous connective tissue deep to the
superficial fascia. Different from the superficial fascia, which is a single, uniform,
continuous layer beneath the skin, the deep fascia is not a continuous layer beneath
the superficial fascia. It is associated with, and in large part brought about by, the
action of muscles in which the fascia forms compartments for the individual muscles
and, with particular muscles, may form part or all of the muscle’s tendon/aponeurosis
of action and attachment. In places as, for example, on the thigh and leg, the tension
created by the action of several muscles results in the deep fascia’s being in several
layers. In this case, there will be sufficient loose connective tissue between the layers
to permit the sliding of the fascial sheets upon one another. For example, the tensor
fasciae latae muscle and biceps femoris muscle insert in common on that part of the
fascia lata (the deep fascia of the thigh) that attaches to the patella, patellar
ligament(s), the tibial tuberosity and cranial margin of the tibia. This same deep fascia
passes superficial to the deep fascia that forms compartments for the muscles of the
leg and inserts on the tuber calcanei and other bony prominences at the tarsus.
The deep fascia, and the fibers of the dermis, are not well developed at birth.
Responding to the different tensions of movement and muscle contraction, they
become stronger throughout life and, in the case of the deep fasciae, appear as a
sheath around many muscles, particularly those of the limbs. When a muscle, which
is basically a fluid suspension, shortens, its volume remains unchanged and the result
is an increase in the girth of the muscle. It is this fact that, in the live animal, lets us
observe the muscle acting in different phases of movement. This swelling of the
muscle during contraction also puts tension on the surrounding connective tissue,
which is gradually transformed from birth into a well-defined sheath around the
muscle. These sheaths have the additional result that, in confining the space in which
contraction and swelling take place, pressure is put on neighboring deep veins and
arteries. Here the result of muscular contraction is chiefly on the thin-walled veins,
which convey the blood at low pressure. The valves in the veins assure that the blood
is directed heartward. With exercise and other muscular activity, the venous return to
the heart is substantially increased and the heart responds by an increased rate and
volume. The large veins in the superficial fascia are also affected this way, the
contraction of neighboring muscles pressing them against the more moderate
resistance of the skin and superficial fascia.
Where bones are just beneath the skin, the superficial and deep fascia fuse with the
periosteum.
Fig. 12. Of the cross-sections of the forearm below, the figure on the right is taken
from Sisson without change. The left figure is the same, modified slightly to
emphasize with a yellow-green color the position of the superficial fascia. In the
section, the deep fascia and the periosteum with which it fuses are deep to the
superficial fascia.
(haired) epidermis
dermis
periosteum
superficial
fascia
deep fascia
Fig. 13. A front view of the shoulder appears as shown in the photo below (this is one
picture that is covered by copyright. You can probably use it for classroom and
personal use, but not for publication or resale without contacting Dreamstime. com):
The musculoskeletal and superficial venous anatomy of the shoulder, arm, and
forearm are shown in the following 3 figures:
the two biceps
tendons of insertion:
one on the radial
tuberosity, one as
the lacertus fibrosus
joins the extensor
carpi radialis tendon.
tendon.d
Fig. 14. This first figure is a deep
dissection. Note that the biceps brachii
arises from the supraglenoid tubercle
and inserts distally on the radial
tuberosity, which is medial on the
proximal forearm. The biceps passes
medial to the humeral crest. The
tendons of the cleidobrachialis and
descending superficial pectoral insert
at the crest, which is palpable. The
brachialis lies in the brachial groove
(sulcus) lateral to the humeral crest.
Distally, it inserts with the biceps on
the proximal medial forearm. The
supraspinatus splits above the
supraglenoid tubercle to insert on the
humerus at the cranial part of the
greater and lesser tubercles.
position of the thick part of the m.
cutaneus colli
m. omotransversarius
m. brachialis
m. cleidobrachialis
m. pectoralis supf. descendens
m. pectoralis supf. transversus
m. ext. carpi radialis
m. ext. digitalis com.
Fig. 15.
Fig. 16. Drawn by
David Stewart Geary
at the University of
Saskatchewan
m. cutaneus colli,
thin part (cut away
where it covers the
ext.jugular vein)
m. sternocephalicus
m. pectoralis supf.,
pars descendens
m. pectoralis supf.,
pars transversus
m. omotransversarius
m. brachiocephalicus,
pars cleidobrachialis
Fig. 17
Fig. 18
The left photograph, which is of an American Quarterhorse, is taken from
Horse Illustrated, August 2012 issue; Bob Langrish is the photographer.
The right figure is drawn by David Stewart Geary after a figure originally
prepared by Hermann Dittrich and the anatomists W. Ellenberger and
Hermann Baum. The thin part of the m. cutaneus colli is not shown in
either drawing.
Fig. 19
Fig. 20
The tendon of origin of the biceps
is palpable, fibrocartilaginous
where it passes over the
intertubercular groove, and bears
a deep sulcus that accommodates
the intermediate tubercle. It is
underlain here by a large bursa.
The belly of the muscle is deep to
the cleidobrachialis and palpable.
It rests on the cranial surface of
the humerus and the humeral
attachment of the coracobrachialis. Inject the bursa by
passing the needle upward, deep
to the muscle belly.
The bicipital bursa of the horse is large. It is separate from the shoulder joint capsule
in this species and must be injected separately. (In the dog, it is an extension of the
joint capsule so that injection of either reaches both.)
Figure 21, below, shows the biceps tendon lifted off the cartilage covered cranial lip of
the proximal end of the right humerus. The picture on the right is taken from The
equine bicipital apparatus - review of anatomy, function, diagnostic investigative techniques
and clinical condition, A. M. MCDIARMID; Equine Vet. Educ. (1999)11 (2) 63-68. It has been
rotated; the original figure is of the left humerus. The photograph of the humerus is
from Sisson.
fibrocartilage of biceps
tendon with deep sulcus
accommodating the
cranial lip
intermediate tubercle
greater tubercle
lesser tubercle
intermediate tubercle
The synovial membrane with the cartilaginous bursal surfaces of the biceps tendon
and of the cranial lip of the proximal end of the humerus enclose a space that
normally is small and the synovial fluid is scant. With inflammation, bursitis, the
synovia (synovial fluid) is increased. The bursal membrane stretches and outpouches
distally.
Blocking of the cutaneous nerves (shown in lateral view in Fig. 22), some of which are
not palpable, may be accomplished by following the border of the muscle from which
they emerge. The lateral cutaneous antebrachial nerve, a branch of the radial,
emerges always in relation to the ventral border of the lateral head of triceps, cranial
to the lateral collateral ligament of the elbow joint. The cranial cutaneous antebrachial
nerve, a branch of the axillary, emerges behind the caudal border of the deltoideus.
The caudal cutaneous antebrachial nerve, the only branch of the ulnar nerve in the
arm, is large enough to palpate. In the horse, the transverse part of the superficial
pectoral is scalloped where it attaches to the medial forearm fascia. The caudal
cutaneous nerve of the antebrachium always emerges beneath the distal border of
the muscle at the indentation of the scallop. This nerve has a large distribution on the
caudal forearm and it may be helpful to block this nerve if the skin is to be sutured.
The medial cutaneous antebrachial nerve, a branch of the musculocutaneous nerve,
emerges between the distal parts of the biceps and brachialis deep to the superficial
pectoral. It is large and readily palpable in the proximal medial forearm where it lies in
relation to the cephalic vein. The nerve crosses the superficial aspect of the lacertus
fibrosus tendon, which in the weight-bearing limb is firm and easily recognized on the
craniomedial side of the upper (proximal) part of the extensor carpi radialis belly. The
nerve can be identified and palpated here as well.
lat. collateral ligament
Fig. 22
Fig. 23, below, is from Handbuch der Vergleichenden Anatomie der Haustiere by
Wilhelm Ellenberger and Hermann Baum; revised 1943, by Otto Zietzschmann, Ernst
Ackerknecht, and Hugo Grau; Springer Verlag. The figure is cropped and modified to
emphasize the scalloped appearance of the transverse superficial pectoral muscle at
its attachment to the medial forearm fascia of the thoracic limb and the emergence of
the caudal cutaneous antebrachial nerve at the indentation of the scallop (in this
figure, the nerve has been added only for the left limb). This scalloped attachment of
the transverse superficial pectoral does not appear in the donkeys that I have
examined; but the nerve is palpable in both of these Equidae.
Figure 24. The medial cutaneous antebrachial nerve is seen in this figure, which is
from Reinhold Schmaltz’ Atlas der Anatomie des Pferdes (published by Richard
Schoetz,1900).
common trunk of musculocutaneous and median nerves
m. biceps brachiilacertus fibrosus
brachiibrachi
m. brachialis, tendon
musculocutaneous nerve
cephalic vein
medial cutaneous antebrachial nerve
m. extensor carpi radialis
In the distal arm, the musculocutaneous nerve departs from its common trunk with the
median nerve. It gives off a muscular branch to the brachialis and sometimes to the
lower biceps brachii (the muscular branch is concealed by the biceps in this figure)
and, as the medial cutaneous antebrachial nerve, extends distally and forward lateral
to the biceps brachii. The nerve emerges distally between the biceps and brachialis,
deep to the superficial pectoral (removed in this dissection). The nerve passes always
superficial to the lacertus fibrosus and can be palpated here upon the strong lacertus
tendon. The nerve is large and supplies the skin of the medial limb distally to the level
of the fetlock joint.
The strong tendon of the superficial, main, part of the infraspinatus can be seen and
palpated as it passes over the caudal part of the greater tubercle of the humerus. This
surface of the greater tubercle is cartilaginous and forms a part of the wall of the
infraspinatus bursa where the tendon rides upon it.
cartilage-covered caudal
part of greater tubercle
supraspinatus attaches here
intermediate tubercle
Fig. 25, from Sisson.
Modified only to show the
cartilage covered part of the
greater tubercle.
point of the shoulder,
cranial part of greater
tubercle
main part of infraspinatus
muscle attaches here
Fig. 26
Figs. 26
Fig. 27
and 27. The “bump” at the end of the arrow is
the infraspinatus tendon as it rides over the cartilage-covered surface of the caudal
part of the greater tubercle. The photo used here, Fig. 27, is a cropped part of the
picture below, which is from www.freebigpicture.com. The picture is rotated from this
original to correspond to the left lateral view of the drawing. The drawing, Fig. 26, is
by David Stewart Geary, Medical Illustrator at the Western College of Veterinary
Medicine, University of Saskatchewan.
Fig. 28