. A manual of diseases of the nervous system. lysis of the tra-pezius; progressive mui«cnlar atrophy. 36 ACTION AND PARALYSIS OF MUSCLES. scapula at rest, but often there is slight rotation (lower angle in) from theunopposed tone of the rhomboids. When the arm is moved forwards by theanterior part of the deltoid, the scapula, no longer held against the thorax andmoved forwards by the serratus, is rotated on its vertical axis by the action ofthe anterior part of the deltoid on the humerus, and of the middle part on thescapula. Thus the posterior edge recedes from the thorax, leaving a grooveint
. A manual of diseases of the nervous system. lysis of the tra-pezius; progressive mui«cnlar atrophy. 36 ACTION AND PARALYSIS OF MUSCLES. scapula at rest, but often there is slight rotation (lower angle in) from theunopposed tone of the rhomboids. When the arm is moved forwards by theanterior part of the deltoid, the scapula, no longer held against the thorax andmoved forwards by the serratus, is rotated on its vertical axis by the action ofthe anterior part of the deltoid on the humerus, and of the middle part on thescapula. Thus the posterior edge recedes from the thorax, leaving a grooveinto which the hand can sometimes be placed (Fig. 8). The scapula is at thesame time rotated, lower angle inwards and upwards. Elevation of the armabove the level of the shoulder is much weakened, but can be imperfectlyeffected by the middle part of the trapezius. Loss of the serratus weakensother movements, but does not abolish any. Inspiratory expansion of the thorax,when the arms are raised, is distinctly less on the paralysed side (Poore).. Fig. 8.—Paralysis of the serratus magnus; FiG. 9.—Paralysis of right deltoid; ele^eversion and rot;ition of scapula when vatiou of shoulder by trapezius on anthe arm is put forwards. attempt to raise the arm, which is slightly abducted by the supraspiuatus. The Deltoid (circumflex nerve, from the brachial plexus posterior cord—C. 4and 5) abducts the humerus, the anterior and posterior fibres also moving the armforwai-ds and backwards respectively. The arm is raised least by the posterior,and most by the anterior fibres, but even the latter only elevate it to a rightangle with the trunk. Hence, if raised by the anterior fibres, and then movedback by the posterior, it is at the same time depressed. Elevation above aright angle is by rotation of the scapula (trapezius and serratus). Thesemuscles also fix the scapula for the deltoid, preventing the rotation (acromiondown, lower angle in) that the deltoid acting alone would cause. In para
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