Biceps

BICEPS (from the Latin bis-twice and caput-head), two-headed, the name of muscles that originate with two separate portions (heads) uniting into a single muscle belly.—Musculus B. brachii (biceps muscle of the arm) with the initial tendon of its long head attaches to the supraglenoid tubercle of the articular cavity of the scapula (tuberositas supraglenoid. scapulae), passing in the intertubercular groove (sulcus intertubercularis) of the humerus, enclosed in a sheath representing a protrusion of the shoulder joint capsule; the short head originates from the coracoid process of the scapula (proc. coracoideus); approximately at the middle of the arm, both heads fuse into a common belly, attaching by a terminal tendon to the tuberosity of the radius (tuberositas radii); the lacertus fibrosus (Pirogov's fascia) separates from it, dividing the basilica vein from the brachial artery (a. brachialis) and the median nerve (n. medianus), and weaves into the fascia of the forearm. The edges of the muscle are marked by grooves; the brachial artery, median nerve, and basilica vein are constantly found in the medial one; the artery is easily ligated in the bend of the elbow, medial to the terminal tendon of the muscle. With the hand in the position of supination, the biceps muscle is a strong flexor in the elbow joint; in the pronated position, it is a supinator (especially the short head). It is innervated by branches of the musculocutaneous nerve (n. musculocutaneus). Variations are very frequent and come down to an increase in the number of heads up to three (with the 3rd most often originating from the diaphysis of the humerus) and to additional terminal attachments of the muscle tendon.—Biceps femoris (biceps muscle of the thigh) with its long head originates, together with the semitendinosus muscle (m. semitendinosus), from the ischial tuberosity (tuber ischiadicus), the short head from the linea aspera of the femur (lin. aspera); the terminal tendon attaches to the head of the fibula (capitulum fibulae), the lateral epicondyle of the tibia (epicondylus lat. tibiae), and the fascia of the leg. When the pelvis is fixed, this muscle is a strong flexor in the knee joint; with a bent knee, it is an outward rotator of the leg; with a fixed leg, it is an extensor in the hip joint. The short head is innervated by the peroneal nerve (n. peronaeus), the long head by the tibial nerve (n. tibialis).—M. biceps surae is a synonym for the gastrocnemius muscles.

The biceps reflex is elicited by percussion of the tendon of the biceps muscle of the arm (m. biceps brachii). The arm should be slightly bent at the elbow. The motor effect of the reflex consists in flexion of the forearm. The reflex arc passes through the IV, V, and VI cervical segments. In the norm, the reflex is constant. Its extinction indicates a lesion of the gray matter of the spinal cord, the anterior or posterior roots in the region of the indicated segments, or the corresponding peripheral nerves. In lesions of the pyramidal system, the biceps reflex, like all other tendon reflexes, is increased.