AXILLA (surgical anatomy)—(Fr. Aisselle, Ger. Achselgrube.) Syn. region axillaire, Velp. is the Latin name for the armpit, and is used by anatomists to designate an important region situated between the upper extremity and the thorax.
The axilla in man is the seat of so many diseases and accidents ; it contains so large a number of nerves, arteries, and lymphatic glands ; and is so frequently interested in sur gical operations, that a pretty full description of it is allowable on the present occasion.
When the arm is separated a little from the side, we observe, in the angle between them, a hollow space, which, in the adult, is always covered with hair. This is, in popular lan guage, the armpit ; but to the anatomist the term axilla conveys a very different notion. By him it is understood to mean a large region, bounded anteriorly by the greater and lesser pectoral muscles, posteriorly by the subsca pular, the Ceres major, and a part of the latis simus dorsi, and internally by the ribs, the intercostal muscles, and the serratus magnus. It presents a basis below, formed of skin and fascia, and an apex above, which opens into the cervical region between the clavicle, scapula, and first rib. Its walls form, therefore, a kind of triangular pyramid, very unequal in their extent, very irregular, and continually under going alterations in size and shape. Its height is greater in the male than in the female, but its other dimensions are nearly equal. It is to be found in all animals which have an upper extremity, and its uses are subservient to the motions of that limb.
In the following description the adult male axilla is always supposed to be meant unless otherwise specified.
When the arm is raised to the horizontal position, we see the floor of this region, the base of our pyramid. This floor is triangular, having its truncated apex at the humerus, its base at the side of the thorax, and its sides formed by the folds of the axilla, that is, the great pectoral in front, the teres major and latissimus behind. It is concave, the concavity looking downwards and outwards. The skin is fine, covered with hair at its upper part from the time of puberty, and secreting, by numerous follicles, a fluid of a peculiar odour.
By raising the elbow higher than the head we convert the concave into a convex, the folds of the axilla are removed, the skin made tense, and the head of the humerus by descending is made to touch the floor of this region. Press ing the arm close to the side lowers the floor, shortens the margins, and relaxes all the parts composing the axilla. When the elbow is drawn a few inches from the side, the axillary artery and nerves may be felt along the humerus, and the head of this bone may be distinguished. In searching for disease in the axilla the arm must be placed in all these positions, but we are most likely to detect any abnormal condition of the parts when the elbow is drawn a few inches from the side, and sup ported without any effort of the patient.
Immediately under the skin we find some cellular substance, containing a small quantity of fat; and next a fascia of considerable thick ness, which gradually loses itself on the side of the thorax, in the general superficial fascia of the trunk. It will be found extremely variable in different subjects, according to the embon point of the individual, sometimes loaded with fat, at other times thin, firm, and somewhat aponeurotic, with its principal bands stretched across from the anterior to the posterior wall of the axilla. In raising it, layer after layer may be removed, until it opens up into that ex tremely lax cellular tissue which attaches itself to the walls of the axilla, loosely supporting glands, vessels, and nerves, and permitting all the motions of which this part is capable. It is obviously cellular membrane. When enlarged glands, or abscesses, or tumours of any kind, form under it, it readily yields, and stretches before the distending force, never exerting any painful pressure on them. The cellular tissue under it is very loose. Numerous vessels ra mify through it which are chiefly derived from the thoracica alaris artery. These vessels are occasionally ruptured, when extensive ecchy moses ensue. Matter formed here passes easily from one part to another, and gives rise to obstinate sinuses, not easily remedied on account of their length and tortuous course.