MANUAL

OF

PRACTICAL ANATOMY.

THE UPPER LIMB.

THE 'HE dissector of the upper limb begins work on the third day after the subject has been placed in the dissecting-room. He will then find the subject stretched out at full length upon its face, with the pelvis and chest supported by blocks (Fig. 1); and while the body remains in this position he must examine those structures which connect the limb to the posterior aspect of the trunk.

Surface Anatomy.-Before proceeding to the actual dissection of any region, the student should make it an invariable rule to familiarise himself with the bony prominences within its area. It is by using these as landmarks that the surgeon is enabled to establish the position of the component parts of the body in the living subject. Their importance can hardly be exaggerated. In the middle line of the back there will be little difficulty in recognising the spines of the vertebræ, which follw each other in consecutive order. If the finger be passed over them, it will be observed that they do not, in every case, occupy the mesial plane;

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one side or the other.

some of them may be deflected, in a slight degree, to The spines of the vertebræ are the only parts of the vertebral column which come to the surface; they alone yield direct information, by touch, to the surgeon as to the condition of the spine. At the lower end of the neck, the spine of the seventh cervical vertebra (vertebra prominens) makes a visible projection; and the spines of the first two dorsal vertebræ are likewise very prominent. As a rule, the most evident of the three is that of the first dorsal vertebra. At a lower level, in subjects of good muscular development, a mesial furrow is produced by the prominence of the erector spinæ muscle on each side, and the spines of the vertebræ may be felt at the bottom of this groove. It attains its greatest depth in the upper part of the lumbar region, and it fades away below at the level of the spine of the third sacral vertebra. The finger should next be passed along the crest of the ilium as it pursues its sigmoid course forwards and outwards. Note that the posterior superior spine of the ilium lies in a slight depression on a level with the second sacral spine. The scapula is for the most part thickly covered by muscles; but, in spite of this, its general outline can be made out. The scapula covers a considerable area on the upper portion of the chest on its posterior aspect. With the hand by the side its superior angle corresponds with the second intercostal space, whilst its inferior angle reaches down as far as the seventh, or even the eighth, rib. It is very mobile-moving more or less with every movement of the limb. The spine and acromion process of the scapula will be seen to be subcutaneous throughout. It is important to make out accurately the angle which is formed by the meeting of the lower border of the spine with the outer margin of the acromion. This very apparent bony point is selected by the surgeon as the upper limit in making measurements of the limb.

DISSECTION OF THE BACK.

In this dissection the following are the parts which require to be examined :

1. The cutaneous vessels and nerves of the back.

2. The trapezius muscle.

3. The latissimus dorsi muscle.

4. The rhomboid muscles and their nerve of supply.

5. The levator anguli scapula muscle.

6. The spinal accessory nerve and the nerves from the cervical plexus which supply the trapezius.

7. The transversalis colli artery and its two terminal branches (viz. the posterior scapular and the superficial cervical).

8. The posterior belly of the omo-hyoid muscle.

9. The suprascapular artery and nerve.

This dissection must be completed in two days, in order that the dissector of the head and neck may be enabled to continue the deeper dissection of the back. The first day's work should comprise-(1) the reflection of the skin; (2) the dissection of the cutaneous nerves and vessels; and (3) the cleaning of the latissimus dorsi and trapezius muscles. The remainder of the dissection can be undertaken on the second day.

Reflection of the Skin. The following incisions are necessary :— 1. From the tip of the coccyx upwards, along the middle line of the body to the spine of the seventh cervical vertebra. 2. From the upper end of the foregoing mesial incision transversely outwards, to the inner border of the acromion process of the scapula. 3. From the lower extremity of the mesial incision in a curved direction outwards and forwards, along the crest of the ilium, to within two inches of the anterior superior iliac spine. 4. An oblique incision from the spine of the first lumbar vertebra, upwards and outwards, to the outer border of the acromion process. The two large flaps which are now mapped out upon the back must be carefully raised from the subjacent fatty tissue. Reflect the upper triangular flap first, and then deal in the same way with the lower flap.

Superficial Fascia.—The fatty layer which is now exposed is termed the superficial fascia. It constitutes the cushion upon which the skin rests, rounds off the angularities of the body, and varies in thickness according to the obesity of the subject. In subjects that have lain for some time on the back it is usually more or less infiltrated with fluid which has gradually gravitated into its loose meshes. The superficial fascia constitutes the bed in which the cutaneous vessels and nerves ramify before they enter the skin; and it is separated from the muscles by a tough, but thin, layer of fibrous tissue, devoid of fat, which forms an investment for the body. This aponeurotic membrane receives the name of the deep fascia; it can be readily demonstrated by making an incision in the superficial fascia, and raising a small portion of it.

Dissection. In searching for a cutaneous nerve, cut boldly down through the superficial fascia in the direction in which the nerve runs, until the plane at which the superficial and deep fasciæ blend is reached. It is here that the main trunks are to be found; and in a well-injected subject the cutaneous arteries constitute the best guides. A more rapid way of finding the cutaneous nerves in this region is to reflect in one layer both the superficial and the deep fascia outwards from the vertebral spines. The nerves are seen piercing the muscles. This plan, however, should only be adopted by the senior student.

Cutaneous Vessels and Nerves.-The cutaneous nerves

of the back are derived from the posterior primary divisions of the spinal nerves. As the latter pass backwards, they

divide into external and internal branches. Both of these supply twigs to the muscles amongst which they lie; but one or other also contains some sensory fibres which come to the surface to supply the skin.

In the dorsal region the upper six or seven cutaneous nerves are the terminations of the internal branches of the posterior primary divisions of the spinal nerves. They become superficial close to the vertebral spines, and are to be sought for near the mesial plane. It is not uncommon to find one or more of them piercing the trapezius one or two inches external to the line of emergence of the others. The branch which comes from the second dorsal nerve is the largest of the series; and it may be traced outwards beyond the spine of the scapula. The lower five or six cutaneous nerves in the dorsal region are the terminal twigs of the external branches

of the posterior primary divisions of the spinal nerves; and, consequently, they must be looked for at a short