Encyclopaedia Britannica > Volume 3, Anatomy-Astronomy

ANATOMY.
Speckl § 6. The Thoracic Extremities.
Anatomy.
The superior or thoracic extremities consist of the
Thoracic sj10U](ier, the arm, the fore-arm, the wrist, and the hand.
ties'"61111" The shoulder consists of two bones,—the scapula or
shoulder-blade, and the clavicle or collar-bone.
The sea. The scapula is a triangular bone occupying the posterior
pula. part of the chest, having a dorsal and a costal surface,
and a superior, a vertebral, and an axillary margin.
The dorsal or posterior surface (dorsum) is divided by
a transverse elevated spine into two parts, the fossa supra-
spinata for the supraspinatus muscle, and the fossa infra-
spinata for the infraspinatus muscle. The latter is con¬
cave above, convex in the middle, and concave towards
the axillary or external margin (costa), from which it is se¬
parated by a round line or crest for the attachment of
the fascia which separates the infraspinatus from the teres
major and minor. Between this crest and the axillary
margin above is a convex surface, of a triangular shape,
with the apex above, for the attachment of the teres mi¬
nor, and below a flat quadrilateral surface for the teres
major.
The spine is a triangular-shaped eminence, rising
obliquely from the upper fourth of the dorsal surface; low
at the vertebral, elevated at the axillary margin, where it
terminates in a broad, flat surface, also triangular, named
the acromion or shoulder-top. In the posterior margin of
the spine may generally be distinguished two surfaces
separated by a ridge. Above the ridge the cucullaris
is fixed; below, part of the deltoid is attached; and be¬
tween is a common aponeurosis. The ridge is biparted
towards the acromion, leaving an interval covered by pe¬
riosteum and integuments only. The anterior part of the
acromion presents a cartilaginous facette, for articulation
with the acromial end of the clavicle. To its posterior
and external margin the deltoid is attached, and to its tip
the acromio-coracoid ligament is fixed.
The costal or anterior surface is of a triangular shape,
with the apex below, generally concave, but subdivided
into smaller spaces by two or more oblique ridges, to
which intermuscular fascice are attached. This surface,
which is the subscapular fossa (venter), lodges the belly of
the subscapular muscle, the fasciculi of which are inter¬
posed between the aponeurotic ridges. Near the verte¬
bral margin is an irregular surface, to which, and also to
the margin, the serratus magnus is attached.
The superior margin (costa superior) is thin and point¬
ed behind, where the levator and omohyoid muscles are
attached, and becomes sinuous externally, with a notch
converted by a ligament into a hole for the transit of the
suprascapular vessels and nerves. The inner or axillary
extremity terminates in an elevated hooked process, the
coracoid, to the tip of which are fixed the cora»o-clavicu-
lar ligament, and the united origin of the short head of
the biceps flexor and the coraco-brachialis, to the anterior
margin the small pectoral, and to the posterior the acro¬
mio-coracoid ligament.
The vertebral or posterior margin (costa posterior, basis
of some authors) is thin, and ascends straight to the
spine, giving attachment to the rhomboideus ; then bends
forward, and forms with the superior an angle, to which,
as also to the edge now mentioned, the levator is fixed.
The axillary margin (costa axillaris, sometimes inferior)
is round and broad above, and narrow below. It presents
above, first the glenoid cavity, round at its lower margin,
angular above, hollow, covered by cartilage and synovial
membrane for receiving the head of the humerus. At
the angular point above is a surface for the attachment
ol the long head of the biceps flexor, and the lower
margin presents two tubercular eminences for that of the Special
long head of the triceps extensor. Below this are fixed the Anatomy.
teres minor, the subscapidaris, and the teres major. The la-)ff^r>^J
tissimus dorsi, passing over its lower angle, binds it down.™°™£
The scapula consists chiefly of compact bone, with ^
little cancellated matter interposed. In the subscapular
fossa this becomes completely absorbed, rendering the
bone thin and translucent, sometimes perforated. The
spine, processes, and angles contain cancellated matter.
It is formed from one part for the body of the bone,
with epiphyses for the coracoid process and the margins.
Nutritious holes are generally found in the angle formed
by the spine with the body, and in the axillary margin.
The collar bone or clavicle is a cylindrical bone, alter-Clavicle or
nately incurvated like an f placed at the upper part of the collar bone,
chest, between the sternum and acromion of the scapula.
It has therefore two extremities, a sternal and acromial,
with intermediate body.
The sternal end is triangular, cartilaginous, concave and
convex in opposite directions, surrounded by ligamentous
insertions. The acromial end is flattened and recurved,
presenting a lunated surface for articulation with the
acromion.
The body, with the shape of a triangular prism at the
sternal end, is rounded above for the attachment of the cla¬
vicular portion of the sterno-mastoid muscle, and presents
below a rough surface for the costo-clavicular ligament,
and a sinuated line for the subclavian muscle. Towards
the acromial end, where it is flattened above and below,
it presents before, a surface for the attachment of the
large pectoral and deltoid muscles; behind, another for
the cucullaris; and below, a prominent oblique crest for
the coraco-clavicular ligaments.
Compact in the middle, and cancellated at its extremi¬
ties, the clavicle is developed from a single point.
The arm-bone or humerus (os brachii) is a long cylin-Thc arm-
drical bone, divided into head or scapular end, cubital orbone'
lower end, and shaft or body.
The head presents three eminences, the articular head,
the anterior tuberosity, and the external tuberosity. The
first, which is hemispherical, incrusted by cartilage and sy¬
novial membrane, with the axis oblique to that of the
bone, and articulating with the glenoid cavity of the sca¬
pula, is separated from the bone by a narrow depressed line
named the x\ec\t(collum), in which is fixed the margin of the
scapulo-humeral capsular ligament. The second is a small,
pointed, sometimes bifid eminence, to which the tendon
of the subscapularis is attached. In the external tuberosity
are distinguished three facettes, to the upper of which the
tendon of the supraspinatus, to the middle that of the infra¬
spinatus, and to the posterior the tendon of the teres minor,
are inserted. Between the anterior and the external tube¬
rosity is a longitudinal groove named the bicipital, for the
transit of the long head of the biceps flexor.
The cubital or lower extremity is flattened transversely,
and moulded into different eminences and depressions.
Internally is the inner or ulnar condyle, large and pro¬
minent, for the attachment of the internal lateral liga¬
ment, and a tendon common to the pronator teres, palmaris
longus, flexor sublimis, radialis internus, and ulnaris inter-
nus. Externally is the outer or radial condyle, to which
are attached the external lateral ligament, and the ten¬
don common to the supinators and extensors, viz. supina¬
tor longus and brevis, anconeus, radialis externus, ulnaris
externus, and extensor communis. Between these is an
articular surface covered by cartilage, moulded into the
small head which moves in the cavity of the radius, a
groove corresponding to the margin of the latter; the
semicircular crest interposed between theratfmsand w/wcz,