By this means the milk-ducts can A cork-lined tray is very useful for this

to unravel the glandular substance. generally be demonstrated. purpose.

Mammary Gland (mamma).—The mammary gland in the female is a smooth rounded prominence, which extends in a horizontal direction from the side of the sternum to the axillary border of the pectoralis major muscle, and in a vertical direction from the third to the sixth or seventh costal arch. It should be clearly understood that it lies within the superficial fascia and that its smooth contour is largely due to the invasion of its substance by the fatty tissue of this layer. It is separated from the great pectoral muscle by the deep fascia, and also by a thin layer of the superficial fascia.

A little below its mid-point, and at a level which usually corresponds to the fourth intercostal space, the mamma is surmounted by a conical elevation--the nipple or mammilla (papilla mamma). This is surrounded by a circular patch of coloured integument, which is termed the areola mammæ. In the nipple, and immediately subjacent to the areola, there is no fat. A curious change of colour occurs in this region during the second month of pregnancy. Of a delicate pink tint in the virgin, the nipple and areola become brown from the deposition of pigment at this time, and they never again resume their original appearance.

Although the mammary gland is placed within the superficial fascia, it is nevertheless completely isolated by a dense fibrous capsule, which sends trabeculæ into its substance. These subdivide the organ into loculi, in which the glandular lobules are placed. From the lobules the ducts (ductus lactiferi) converge towards the nipple. Look for them

particularly in the region of the areola. Here they become much dilated, and form pouches or ampullæ (sinus lactiferi) which serve as temporary reservoirs for the milk (Fig. 5). At the base of the nipple the lactiferous ducts again contract and run forwards in its substance towards its summit, upon which they open.

In a well-injected subject, twigs from the intercostal arteries, and also from the perforating branches of the

internal mammary, may be traced into the mammary gland, and another vessel, called the external mammary artery, may be seen winding round the edge of the greater pectoral muscle, or piercing its lower fibres to reach the gland.

By means of lymphatic vessels the mammary gland is brought into connection with the sternal glands, and also more directly with the axillary glands. The latter connection is one of much importance to the surgeon in cases where it is necessary to remove the organ for malignant disease.

In the male the mamma (mamma virilis) is extremely rudimentary. The nipple is small and pointed, and the areola is surrounded by sparse hairs.

The Deep Fascia of the pectoral region is a thin membrane which closely invests the pectoralis major. It is attached superiorly to the clavicle, and is firmly connected in the middle line to the front of the sternum. Below, it is continuous with the deep fascia covering the abdominal muscles. Its strongest fibres are directed outwards, parallel to the clavicle, and, at the lower border of the great pectoral muscle, it is continuous with the axillary fascia. At the infraclavicular fossa a process from its deep surface dips in to join the costo-coracoid membrane, whilst, beyond this, it becomes continuous with the fascia covering the deltoid muscle. The axillary fascia and the costo-coracoid membrane will be separately described later on.

Dissection. The pectoralis major muscle must now be cleaned, and its division into sternal and clavicular parts clearly made out. The muscular fibres are rendered tense by abducting the arm from the side. On the right side the dissector begins at the lower border of the muscle, whilst on the left side he commences at the upper border. Clean also the anterior margin of the deltoid. In the interval between it and the portion of the pectoralis major which arises from the clavicle, the cephalic vein, and, subjacent to this, the humeral thoracic artery will be discovered.

The Pectoralis Major extends from the anterior aspect

It is divided by a deep

of the chest to the humerus. fissure into a clavicular and a costo-sternal portion. This fissure penetrates through the entire thickness of the muscle, the clavicular and costo-sternal portions being thus distinct, except close to their insertion. The clavicular portion arises by short tendinous and muscular fibres from an impression on the inner half of the anterior surface of the clavicle. The costo-sternal portion takes origin by fleshy fibres from the anterior surface of the sternum, from the aponeurosis of the external oblique muscle, and occasionally from the sixth rib near its cartilage. Under cover of this more superficial origin, and partially independent of it, a variable number of muscular slips spring from the cartilages of the upper six ribs.

The pectoralis major is inserted by a flattened bilaminar tendon into the outer lip of the bicipital groove of the humerus (pectoral ridge), and the fibres of the muscle undergo a re-arrangement as they converge upon this tendon. The greater part of the clavicular portion joins the anterior lamina of the common tendon; some of the innermost clavicular fibres, however, are inserted directly into the humerus below the tendon, whilst a few gain attachment to the deep fascia of the arm, and become adherent to the adjacent part of the deltoid.

The fibres of the costo-sternal portion of the muscle take different directions as they proceed to join both laminæ of the tendon of insertion; thus the upper fibres descend slightly, the intermediate fibres pass horizontally outwards, whilst the lower fibres ascend, and, at the same time, gain the deep surface of the rest of the muscle. A smooth, full and rounded lower border is in this way formed which constitutes the anterior fold of the axilla. The bilaminar tendon of the pectoralis major is the direct continuation of the axillary fold, and its two lamine are thus united, or, in other words, continuous below. The precise manner in which it is attached will be more fully studied at a later stage of the dissection.

The Axilla may be defined as being the hollow or recess

between the upper part of the side of the chest and the upper part of the arm. When the limb is abducted from the trunk, and the areolo-fatty tissue which occupies the armpit is removed, the space presents a distinctly pyramidal form. The apex, or narrow part of the space, placed immediately to the inner side of the coracoid process, is directed upwards towards the root of the neck, whilst the wider part or base looks downwards. But the space is not absolutely pyramidal in form, for the inner wall formed by the chest is of greater extent than the outer wall formed by the arm. It follows from this, therefore, that the anterior and posterior walls converge as they proceed outwards. Before engaging in the dissection of the space, it is necessary that the student should have some knowledge of its boundaries, and the manner in which its contents are disposed in relation to these.

Boundaries of the Axilla.-The anterior wall is formed by the two pectoral muscles and the costo-coracoid membrane. The pectoralis major constitutes the superficial stratum, and is spread out over the entire extent of the anterior wall. The pectoralis minor, which lies subjacent to the greater pectoral muscle, is only in relation to about one-third of the anterior boundary, whilst the interval or gap between this muscle and the clavicle is filled up by the costo-coracoid membrane. The lower border of this wall of the axilla constitutes its anterior fold, as already explained. This is formed by the lower margin of the pectoralis major, with a small part of the lower border of the pectoralis minor, which comes into view near the side of the chest.

The posterior wall of the axilla is somewhat longer than the anterior wall. It is formed from above downwards by the subscapularis muscle, the tendon of the latissimus dorsi, and the teres major muscle. The subscapularis, lying upon the venter of the scapula, takes by far the largest share in the formation of this boundary. The narrow tendon of the latissimus dorsi lies in front of the teres major, so that only the lower border of the latter muscle is seen below it.

The posterior fold of the axilla is formed by the lower border of this wall.

The inner wall is constituted by the upper four or five ribs with the intervening intercostal muscles; it is clothed by the corresponding digitations of the serratus magnus muscle.

The outer wall is formed by the humerus and the conjoined origin of the coraco-brachialis and short head of the biceps.

The apex of the space corresponds with the narrow

9 10 13 8 4

3

2

FIG. 6.--Diagram of section through the axilla of the left side.

communication between the axilla and the root of the neck. It is a triangular interval (which can readily be investigated by the finger when the space is dissected) bounded by the clavicle, first rib, and upper margin of the scapula, and through it pass from the neck the great axillary vessels and brachial nerves. The wide vaulted base of the armpit is closed by the axillary fascia.

Contents of the Axilla.-The axillary artery and vein, with the great brachial nerves, constitute the most important contents of the armpit. Except at the summit of the space, they lie closely applied to the outer wall, and follow it in all