Bicipital aponeurosis

The bicipital aponeurosis (also known as lacertus fibrosus) is a broad aponeurosis of the biceps brachii which is located in the cubital fossa of the elbow and separates superficial from deep structures in much of the fossa.

The bicipital aponeurosis originates from the distal insertion of the biceps brachii. While the tendon of the biceps inserts on the radius, the aponeurosis stretches from the medial side of the biceps tendon and passes obliquely downward and medially across the brachial artery. It is continuous with the antebrachial fascia covering the origins of the flexor muscles of the forearm.

The aponeurosis reinforces the cubital fossa, and helps to protect the brachial artery and the median nerve running underneath. This protection is important during venipuncture (taking blood) from the median cubital vein.

Some individuals (about 3% of the population) have a superficial ulnar artery that runs superficially to the bicipital aponeurosis instead of underneath it. These individuals are at risk for accidental injury to the ulnar artery during venipuncture.