From the above described attachments of the tendons of the biceps and brachiwus an ticus to the aponeurosis of this region, it fol lows as a necessary consequence that the con tractions of these muscles must have the effect of rendering it more tense.
The aponeurosis of the arm assumes the form of a very thin fascia as it approaches the superior margin of the expansion of the biceps ; at this place it often appears to degenerate into cellular tissue which covers an oval space placed obliquely, the broader extremity of which is below, being bounded by the expan sion of the biceps externally and inferiorly, and by a sort of defined border terminating the lower margin of the brachial aponeurosis superiorly and internally : in this oval space the brachial artery and the median nerve which lies to its inner side are more thinly covered than in any other part of their course. The aponeurosis is also very weak on the external side of the expansion of the biceps, where it is pierced by the deep branch of the median vein, and by the external cutaneous nerve which comes from beneath the aponeurosis at this place.
The brachial artery terminates by dividing into the radial and ulnar arteries in the tri angular depression, which is bounded exter nally by the supinator longus and internally by the pronator radii teres.
This artery enters the region of the elbow on the internal side of the tendon of the biceps included in a common sheath with its two venm comites, one of which lies on either side of it; it lies on the surface of the brachiwus anticus, and, becoming deeper as it descends, it divides into the radial and ulnar arteries at about an inch below the level of the internal condyle. The median nerve lies internal to it, separated from it at first by cellular tissue ; lower down, where this nerve pierces the pro nator teres, the external origin of that muscle arising from the coronoid process is interposed between it and the artery : the radial and ulnar arteries, while still in this region, give off their recurrent branches, which pass upwards, encir cling the condyles of the humerus, to anasto mose with the profundm and anastomotic branches of the brachial, as described in the article BitAcutAL AwrEay. The venm comites of the brachial, radial, and ulnar arteries are double : these vessels are also accompanied by a deep set of lymphatics. The nerves which traverse this region beneath the aponenrosis are, the median on the internal side of the brachial artery; the radial, which, descending between the brachhrus anticus and the supinator radii longus, then between the biceps and ex tensor carpi radial is, into two branches, the posterior of which passes between the supi nator brevis and extensor carpi radialis brevior to the muscles on the back part of the fore-arm, while the anterior branch or proper radial nerve descends in the fore-arm under the su pinator radii longus. The trunk of the ulnar nerve passes behind the internal condyle, and entering between the two heads of the flexor carpi ulnaris follows that muscle down the fore-arm.
Development.—In early life the condyles of the humerus are not so well marked, nor is the olecranon so prominent, in consequence of which extension of the elbow can be carried farther than in the adult. At the same period
the lesser sigmoid cavity of the ulna is pro portionally smaller, and the annular ligament of the radius much more extensive.
l'arietics.—When a high division of the brachial artery takes place, it often happens that the radial artery takes a superficial course, sometimes under and occasionally over the aponeurosis to its usual destination. The pos sibility of this occurrence should be constantly held in recollection in performing phlebotomy in this region, as it is evident that the vessel, when thus superficially situated, is exposed to be wounded by the lancet of the operator.
In considering the relative advantages pre sented by each of the superficial veins which may be selected for phlebotomy, it is necessary to remark that the operation may be performed on any of the veins at the bend of the arm ; on the cephalic and basilic veins it is un attended with any danger ; not so, however, when either the median basilic or median cephalic is the vessel selected. When bleed ing in the median basilic vein about the mid dle of its course, if the lancet should transfix the vein, there is danger of the instrument wounding the brachial artery, an accident of serious consequence; the risk of this accident is not so great when the vein is opened near its lower part, as the brachial artery retires from it here towards the bottom of the trian gular depression of the elbow ; besides the occasional risk of wounding the radial artery, which, in consequence of a high bifurcation of the brachial, sometimes follows the super ficial course already alluded to, the branches of the internal cutaneous nerve may be wholly or partially divided; in which latter case sharp pains are usually felt extending along the course of these nerves. Opening the median cephalic vein may be performed without ap prehension of injury to the brachial artery; the external cutaneous nerve however, the trunk of which lies behind this vein, may suffer a puncture, in consequence of the lancet being pushed too deeply, the consequences follow ing which have been in many instances a pain ful affection extending along the branches of this nerve to their terminations. In those un fortunate cases in which the brachial artery is punctured, should the wound in the artery not be closed and united by properly regulated pressure, the consequence likely to ensue may be one of the following : I, the blood escap ing from the wound in the artery may become diffused through the cellular membrane of the limb extending principally upwards towards the axilla along the sheath of the vessel, ( the diffused false aneurism ;) 2, the blood which escapes from the artery may be circumscribed within a limited space by the cellular mem brane which surrounds it becoming condensed, (the circumscribedfillse aneurism ;) 3, the wounded orifices of the artery and vein may remain in apposition, and adhere to each other, allowing the blood to pass from the artery directly into the vein, constituting the affection called aneurismal variv ; 4, or a circum scribed sac may be formed between the artery and vein, having a communication with both vessels, the varicose aneurism.
(J. hart.)