process of the atlas. These muscles move the head on the atlas and the atlas on the axis. They are supplied by the posterior branch of the first cervical nerve.

MUscLEs OF THE TRUNK.-The trapeziums has already been described as a superficial muscle of the upper part of the back; in the loin region the latissimus dorsi (fig. 5) is the superficial muscle, its origin being from the lower thoracic spines, lower ribs and lumbar forming the semisplnalis and multijidus spinae muscles. The latissimus dorsi and rhomboids are supplied by branches of the brachial plexus of nerves, while the deeper muscles get their nerves from the posterior primary divisions of the spinal nerves (see NERVE, SPINAL). On the anterior part of the thoracic region the peetoralis major runs from the clavicle, sternum and ribs, to the humerus (fig. 6); deep to this is the pecloralis minor, passing from the upper ribs to

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""""LEXUS

ST0lD

SPLENIUS QAPITIS

SPL:-:Nina coLr.r-SERRATUS

Posrrcus SUPERIOR

Levnrok ANcU1.1

BOIDE

Rnomaomnus

MAJOR

MAj

Vertebral

aponeurosis

Larxssmus

Srmno-uasrom

TRAPEZIUS

Dm.rouJ

Rnomsomsus

MAJOR

MA lOl

Lfxnssnms

nous;

Ssnmxrus posrrcvs

run-muon ms axremvvs

umommxs

Onuouus Exrenuus

Asoomms —

-OBLIQUUS nrnannvs

OBLIQUUS mruumxs

Fascia over gluteus

maximus

fascia

Fascia over gluteus

maximus (cut)

SMAXDIUS

From A. M. Paterson, Cunningham's Tex! Book of Analomy. FIG. 5.-Superficial Muscles of the Back. fascia, and it is inserted into the upper part of the arm bone or humerus. When the trapeziums is cut, the rhomboid muscles (major and minor) passing from the upper thoracic spines to the vertebral border of the scapula are seen, and deep to these is theserralus posticus superior passing from nearly the same spines to the upper ribs. On reflecting the latissimus dorsi the serralus poslious inferior is seen running from the lower thoracic spines to the lower ribs. W'hen these muscles are removed the great mass of the ereelor spinae is exposed, familiar to every one as the upper cut of the sirloin or ribs of beef; it runs all the way up the dorsal side of the vertebral column from the pelvis to the occiput, the com plexus already mentioned being its extension to the head. It is longitudinally segmented into many different bundles to which special names are given, and it is attached to the various vertebrae and ribs as it goes up, thus straightening the s ina] column. Deep to the erector spinae are found shorter bundles passing from one vertebra to another and the coracoid process. The serratus mognus is a large muscle rising by serrations from the upper eight r1bs, and running back to the vertebral border of the scapula, which it draws forward as in the fencer's lunge. Between the ribs are the external and internal intercostal muscles; the former beginning at the tubercle and ending at the junctions of the ribs with their cartilages, while the latter only begin at the angle of the ribs but are prolonged on to the sternum, so that an interchondral as well as an intercostal part of each muscle is recognized. The fibres of the external intercostals run downward and forward, those of the internal downward and backward (see RESPIRATION). The abdominal walls are formed of three sheets of muscle, of which the most superficial or external oblique (fig. 6) is attached to the outer surfaces of the lower ribs; its fibres run downward and forward to the pelvis and mid-line of the abdomen, the middle one or 'internal oblique is on the same plane as the ribs,

and its fibres run downward and backward, while the tmnsversaus