The upper limb is attached to the back of the trunk by five muscles, the trapezius and the latissimus dorsi, which are attached to the scapula and to the humerus, and cover nearly all the back from the occiput to the ilium. Underneath the trapezius are the two rhomboid muscles, and the levator anguli scapulae. The latissimus dorsi, with the teres major, form the posterior fold of the axilla. The pectoralis major, which extends from the anterior aspect of the sternum to the pectoral ridge of the bicipital groove of the humerus, forms, with the lower border of the pectoralis minor, the anterior fold of the axilla. These two muscles and the subclavius and serratus magnus attach the upper limb to the front of the trunk. The lower limb is attached to the trunk by psoas, iliacus, pyriformis, and gluteus maximus muscles.

There are five layers of muscles on the back. The first two, as above mentioned, are connected with and act on the upper limb.

Of the third layer, two are muscles of respiration. The third keeps the head erect.

The fourth layer is composed of the erector spinae and its continuations, the long extensors of the back, extending from sacrum to occiput. They keep the back erect.

The fifth layer is composta of many small muscles, lying in the groove between the lateral and spinous processes, the entire length of the column.

The front of the abdomen is closed in by five pairs of muscles ; in the middle are two recti, which are parallel to the middle line, with the two pyramidales at their lower end. At the sides are the external oblique, the fibres of which run downward and forward ; the internal oblique immediately under the external—its fibres run upward and forward ; and the transversalis under the internal oblique—its fibres run across. This arrangement of the fibres gives strength to the abdominal walls.

Fig. 69.—Superficial Muscles of the Back. 1, Trapezius; 2, sterno-mastoid ; 3, latissimus dorsi; 4, external oblique.

Fig. 70.—Deep Muscles of the Upper Part of the Back.

1, Complexus; 2, splenius ; 3, serratus posticus superior; 4, levator scapulae ; 5, cervicalis ascendens ; 6, transversalis cervicis.

These three muscles become tendinous towards the middle, and unite with their fellows of the opposite side, forming an incomplete sheath for the recti muscles. A fibrous band is formed in the middle line by their union, reaching down from the ensiform cartilage to the pubes ; it is called the linea alba.

Fig. 71.—Superficial Muscles of the Abdomen. 1, Rectus abdominis; 2, external oblique; 3, linea alba.

The thickened lower border of the external oblique muscle is folded back on itself, and forms Poupart's ligament. It is attached to the anterior superior spine of the ilium and to the pubis. The lower border joins the fascia lata of the thigh.

Fig 72.—Muscles of the Pelvis.

1, Quadratus lumborum ; 2, psoas parvus ; 3, psoas magnus ; 4, iliacus ; 5, pyriformis ; 6, obturator externus.

The round depressed cicatrix between the ensiform cartilage and the pubis, nearer to the latter, is the umbilicus.