ELBOW, REGION OF TIIE ; fold or bend of the arm. (Fr. pli du bras; cuticle.) The region of the elbow is situated at the angular union of the arm with the fore-arm, and con tains the humero-cubital articulation and the various organs which surround it : the extent of this region may be determined, superiorly by a circular line at a finger's breadth above the internal condyle, and inferiorly by a similar line at two fingers' breadth below that process: its greatest extent is in the transverse direction, and it forms an angle salient posteriorly and retiring in front, which cannot be effaced even in the utmost extension of the fore-arm. The anterior surface of this region when examined in the arm of a muscular man presents a triangular depression, in which is observed the confluence of several large subcutaneous veins ; the base of this depression is above ; the sides are formed by two prominences, of which the ex ternal is larger and more marked than the in ternal, and the apex of the triangle is formed inferiorly by the convergence of these pro minences, which consist of the two masses of the muscles of the forearm which arise from the condyles of the humerus. This triangular depression is divided superiorly into two por tions by a prominence formed by the tendon of the biceps; in the external or larger portion the median cephalic vein is situated, the in ternal is occupied by the oblique course of the median basilic vein and the trunk of the brachial artery, the pulsations of which can usually be felt and are even sometimes visible in this space: the superficial radial or cephalic vein and the two ulnar veins which contribute to form the basilic are also apparent in this region, being situated over the lateral mus cular prominences. In the arm of a corpulent female, instead of the appearances here de scribed, the front of the elbow presents a semilunar fold or depression, the concavity of which embraces the prominence formed by the biceps.
Laterally, the region of the elbow presents two prominences formed by the condyles of the humerus, of which the internal is more marked and higher than the external : in the arms of corpulent persons, on the contrary, two depressions like dimples are placed over the condyles.
Posteriorly, the olecranon forms a remark able prominence, the situation of which varies in its relation to the condyles of the humerus according to the different motions of the fore arm ; in complete extension it is above the level of these processes, in semiflexion it is on the same level with them, and is below them when the elbow is flexed to a right angle.
On either side of the olecranon there is a depression of which that on the internal side is more marked ; pressure here produces a painful sensation which is felt in the little finger and the inner side of the ring-finger; in the depression external to the olccmnon the posterior edge of the head of the radius can be felt rotating immediately below the external condyle when pronation and supination of the fore-arm are performed. An accurate know ledge of the relations of these parts is essential to the forming an accurate diagnosis in cases of fractures and dislocations in this region.
Skin and subcutaneous tissue. — The skin covering this region is thin, smooth, and de licate in front ; it is furnished with hairs over the lateral prominences, where it also contains sebaceous follicles in greater numbers than over the anterior depression. In consequence of being very vascular mid plentifully supplied with nerves, the skin here is prone to intlam mation, and is often the seat of small plilegmo and of erysipelas. Posteriorly the skin is thicker, rough on the surface, and generally thrown into transverse folds above the olecranon, particularly in extension : it abounds more in sebaceous follicles and hairs here than on the anterior surface. The sub cutaneous cellular tissue in front consists of two layers: one of these, more deep-seated, forms a sort of fascia, between the layers of which the subcutaneous veins and nerves are situated; the other, superficial, is principally composed of adipose tissue and varies very much in thickness. In lean persons this latter layer is often of extreme tenuity ; while the other, on the contrary, is then thicker and more closely adherent to the skin. This deeper layer is considerably thicker over the anterior angular depression than on the lateral pro-. minences: it sinks in between the pronator radii teres and supinator longus in company with the deep median vein, and is continuous with the cellular tissue between the muscles and around the articulation. Posteriorly the subcutaneous cellular membrane is more loose and lamellar : adipose tissue is almost always absent in it over the condyles of the humerus, and on the smooth posterior surface of the olecranon, there is merely a subcutaneous bursa mucosa between the skin and the peri osteum.