Illustrated Encyclopedia of Human Anatomic Variation: Opus III: Nervous System
Ronald A. Bergman, PhD
Adel K. Afifi, MD, MS
Ryosuke Miyauchi, MD
Peer Review Status: Internally Peer Reviewed
Abstract. In 158 brachial plexuses the origin of the fibers of the ulnar nerve - whether only from the medial or also from the lateral fascicle - was investigated. A lateral root was found in 56%. This lateral root may either be accompanied by fibers of the median nerve (type 1) or may run separately (type 2). Where this root crosses the medial root of the median nerve, either a small minority of fibers of the latter nerve may run behind the ulnar fibers (type a), or all median fibers are in front of them (type b). Considering the relation 56:44% between ulnar nerves with and without a lateral root both possibilities have to be considered as normal variations, none as a variety. In analogy to the term 'median loop' the term 'ulnaris loop' is suggested for specimens with a lateral root.
Different origins of Type 2 lateral roots of the ulnar nerve. l= lateral root, m=medial root, M=median nerve, u=ulnar nerve
Fuss, F.K. Acta Anat. 134: 199-205, 1989
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