PART II.

DISSECTION OF THORAX, BACK, AND UPPER EXTREMITY.

CHAPTER I.

THE UPPER EXTREMITY.

SECT. I.-DISSECTION OF THE PECTORAL AND AXILLARY REGIONS.

BEFORE Commencing the dissection of these parts, the student should make himself familiar with the prominent points around the shoulder and axilla. He should also notice the outlines of the thorax, the regions into which it is divided for the purposes of auscultation and percussion, the position of the mamma, and the degree in which these various regions are subcutaneous or covered by muscles.

It will be perceived that the sternum is partly subcutaneous, also the clavicle, with the acromion process, and spine of the scapula. The position of the coracoid process of the scapula should be ascertained, and its relations to the clavicle and acromion process carefully observed. The position of the upper extremity should be varied so as to show the movements of the clavicle and scapula, and any changes which may occur in the general configuration of the parts.

An incision may now be made through the skin and superficial fascia, commencing at the middle of the upper border of the sternum, and extending along the clavicle to the acromion process. Another may then be made along the median line of the sternum, to the xiphoid cartilage; and a third from the sterno-clavicular articulation, to the insertion of the pectoralis major. The skin may now be raised by reflecting one flap towards the shoulder, and the other towards the lower border of the pectoralis major. In case the abdomen is being

dissected at the same time, it may be convenient to carry the last incision from the xiphoid cartilage along the lower border of the pectoral muscle, since the parts belonging to both the upper and lower extremities are here more or less blended. In this way the same incision, as far as the origin of the pectoralis major is concerned, will answer for both. The portion of skin covering the serratus magnus may be left till the student is ready to dissect the axilla, when it may be reflected off in a single flap.

The integument of the pectoral region demands no particular notice.

Its nerves are derived partly from the supra-clavicular, Fig. 103 (1), and supra-acromial, Fig. 104 (1), branches of the cervical plexus, which descend from the neck over the clavicle and sternum, and partly from the anterior cutaneous branches of the intercostals, which perforate the intercostal spaces along the border of the sternum, and ramify in the subcutaneous fascia; a branch of the second intercostal nerve anastomoses with a branch of the supra-clavicular.

Fig. 88.

The cutaneous arteries come from the internal mammary, and from the thoracic branches of the axillary. The largest of them are distributed to the mammary gland. There is only one vein of any importance superficial to the deltoid and pectoralis major muscles, and this is the cephalic, which occupies the groove corresponding to the juxtaposition of these muscles. In removing the skin and fascia, the student should look for this vein and the humeral branch of the thoracico-acromial artery which accompanies it.

The MAMMARY GLAND, Fig. 88, should be examined in situ: its lobulated arrangement; its appearance as contrasted with the surrounding tissues; the manner in which it is connected with the fascia, and its relations to the pectoralis major and the thorax generally.

Its arteries and nerves are derived from the same sources as those of the

skin in its vicinity. Its lymphatics are connected with those

of the axilla, and also with others in the cavity of the thorax.

The size of the gland varies greatly. In the female it is much larger than in the male. The nipple is situated a little to the inner side of the centre. It is surrounded by an areola, the tint of which, in the female, depends on several circumstances, as complexion, menstruation, pregnancy, &c. The surface of the mamma appears smooth, the spaces between the lobules being filled with fat. There is not, however, usually much fat beneath the skin around the nipple.

The lactiferous tubes, Fig. 89, in the nipple, vary from fifteen to twenty-three or four. These tubes are wholly independent of each other; so, also, are the various smaller ducts of the different lobules, which proceed from the radicles, and unite to form them; hence, if one of these tubes shall become closed during lactation, the milk will necessarily be accumulated in all the smaller tubes of which that is a common outlet.

Fig. 89.

There are small glands on and around THICKNESS AND the nipple, for the purpose of supplying a lubricating secretion.

The importance of supporting the mammæ during lactation, and especially if suf fering from inflammation, will be suggested by their position and means of attachment to the thorax.

There is generally very little fat in the subcutaneous fascia or areolar tissue in this region.

THE

ORIGINS OF THE LACTIFEROUS DUCTS.-1, 2, 3. Its pectoral surface. 4. Section of the skin on the surface of the gland. 5. The thin

skin covering the nipand lobes composing

ple. 6. The lobules

the gland. 7. The lactiferous tubes coming

from the lobules. 8.

The same tubes col

lected in the nipple.

The deep or special fascia consist of one investing the pectoralis major, and another covering the deltoid. The pectoral fascia is continuous from the lower border of the great pectoral muscle, across the axilla to the latissimus dorsi; also with the fascia of the arm. Externally, it dips down between the deltoid and pectoralis major muscles, along with the deltoid fascia, which is inserted below into the deltoid ridge, and is

continuous behind with the infra-spinata fascia and that of the arm or the brachial fascia. These fascia should be studied with reference more particularly to the formation of abscesses beneath them.

The deep fascia may now be raised by making an incision through it from the sterno-clavicular articulation to the insertion of the pectoralis major. The student, in this way, will be able to raise the fascia so as to trace its continuity as described above, at the same time that he exposes the pectoralis major. The deltoid fascia may be raised in the same manner from the deltoid muscle, although it will be sufficient to expose only the anterior half of this muscle at the present time.

The PECTORALIS MAJOR, Fig. 90 (7, 10), arises from the inner half of the clavicle, the anterior surface of the sternum, the cartilages of the second, third, fourth, fifth, and sixth ribs, and by a slip from the aponeurosis of the external oblique. From this broad origin the fibres converge, and are inserted, by a flat tendon, into the anterior margin of the bicipital groove on the humerus, and into the brachial fascia. From the extensive origin and narrow insertion of this muscle, the student will see the necessity of the difference which exists in the direction of its fibres, and the effects of different portions of the muscle acting separately. The lower fibres are nearly horizontal, while the upper are vertical in their direction. The upper part of the muscle is inserted lower down than the inferior portion, which causes a sort of doubling of the tendon. The action of this muscle varies; if the clavicular portion alone acts, it will draw the arm upwards and forwards, the sternal will move it directly forwards, while the lower part will draw it downwards and forwards; the entire muscle will bring the arm inwards and forwards. If the humerus be elevated and fixed, then the lower part of the muscle will raise the ribs and draw them outwards so as to assist in expanding the thorax. If the hand be supined, it is capable of pronating it by rotating the humerus inwards. The clavicular portion is usually separated from the costosternal by areolar tissue. This fissure is sometimes quite large, and extends some distance towards the insertion of the muscle; again, it is scarcely perceptible. An areolar interspace also separates this muscle from the deltoid. In this