MUSCLES OF THE PECTORAL REGION. 313 
NERVE SUPPLY. 
he nerves supplying the muscles connecting the upper limb to the trunk are given in the 
Tl upplying the muscl nnecting the 1 limb to the trunk are given in tl 
following table :— 
Muscles. Nerves. Origin. | 
| 
Merits { Spinal accessory nerve Spinal Cord 
| Cervical plexus C33, As 
Latissimus dorsi Long subscapular CG) i. 28: 
Levator scapule f Cervical plexus Chae 7A) | 
' | Posterior scapular Cra: 
3 Rhomboidei Posterior scapular pee: 
] Peerarales { External anterior thoracic Gaon 1G. #7: 
aon | \ Internal = sf CES (Semel yal 
Subclavius Brachial plexus | Ces, Oa. 1s 
Serratus magnus Posterior thoracic Ci (os Os oi. 
ACTIONS. 
The muscles of this group (together with the sterno-cleido-mastoid and omohyoid muscles) act 
for the most part in the movements of the shoulder girdle at the sterno-clavicular and acromio- 
elavicular joits. At the former joimt they produce the various movements of the clavicle on the 
sternum, and cause the shoulder to move in a radius the centre of which is the sterno-clavicular 
joint. At the latter articulation they produce a rotation of the scapula on the clavicle, and a 
consequent alteration in the direction of the glenoid fossa. At the same time the several muscles 
‘are agents in other equally important movements, when the shoulder girdle is fixed ; movements 
of the head and neck ; movements of the trunk and ribs; and, in the case of the pectoralis major 
and latissimus dorsi, important movements of the arm at the shoulder joint. 
1. Movements of the Shoulder Girdle.—The action of this group of muscles on the shoulder 
girdle (mainly corresponding to movements at the sterno-clavicular joint) may be expressed in 
the following table : 
| 
_ a. Movement in a Vertical Plane. _ b. Movement in a Horizontal Plane. | 
3 Elevation. Depression. Forwards. Backwards. | 
| Trapezius (upper Trapezius (lower Serratus magnus | Trapezius | 
fibres) fibres) Pectoralis major _ Rhomboidei 
| Levator scapulee Subclavius Pectoralis minor | Latissimus dorsi | 
Rhomboidei Pectoralis minor Be Ged 2} 
Sterno-mastoid Latissimus dorsi Ele aiglitrs aa). xe _ 
Omohyoid Pectoralis major c. Rotation—a combination of these 
| (lower fibres) muscles. 
-~ 2 Movements of the scapula on the clavicle produce an alteration of the direction of the 
glenoid fossa of the scapula, and are accompanied by movements, inwards and outwards, forwards 
and backwards, of the inferior angle of the scapula. By the combined action of the muscles 
acting upon the shoulder girdle a rotatory movement of the scapula at the acromio-clavicular 
joint is effected, by which the relation of the glenoid fossa to the head of the humerus is preserved 
in movements of the arm. 
3. In forced inspiration, the sterno-mastoid, trapezius, levator scapulee, rhomboidei, sub- 
lavius, omohyoid, serratus magnus, pectoral muscles, and latissimus dorsi, acting together, raise 
nd fix the shoulder girdle; while those of them which have costal attachments—subclavius, 
pectoral muscles, serratus magnus, and latissimus dorsi, simultaneously elevate the ribs and 
expand the thorax. 
4. Lateral flexion and rotation of the spine in the neck is effected partly by the action of 
the trapezius, levator scapula, and rhomboid muscles (with the shoulder fixed). ‘The latissimus 
dorsi and pectoralis major act in climbing in a similar way, raising up the trunk towards the 
shoulder. 
5. Action on the Upper Limb.—By reason of their insertion into the humerus the pectoralis 
major and latissimus dorsi muscles assist the movements of the upper limb. Acting together, the 
two muscles depress the shoulder, and draw the arm to the side of the body, at the same time 
rotating the humerus inwards. The two parts of the pectoralis major have slightly different 
actions on the humerus. The clavicular part of the muscle (portio attollens) draws the arm in- 
wards and upwards; the costo-sternal part of the muscle (portio deprimens) draws it inwards and 
