Coracobrachialis muscle and the musculocutaneous nerve: a study using human embryonic sections

Abstract

Summary: In comparative anatomy, the musculocutaneous nerve is hypothesized to pass between the superficial and deep muscle bellies of the coracobrachialis muscle. The superficial belly is supplied by nerve branches of the lateral cord of the brachial plexus, while the deep belly by the musculocutaneous nerve. Observations of longitudinal sections of ten human embryonic arms (7 weeks; crown-rump length 26-32 mm) demonstrated that the coracobrachialis muscle was always continuous with the short head of the biceps muscle. If the aforementioned hypothesis was applied, the deep belly behind the musculocutaneous nerve course was continuous with the biceps. However, such a close relation between the coracobrachialis and biceps was not known in supplying nerves in adults. A further study using embryos of some apes without the deep belly of the coracobrachialis would be necessary for the comparison between a pattern of the embryonic muscle division and the muscle classification in comparative anatomy.bryos for suitable materials of the present observation. Materials and MethodsThe study was performed in accordance with the provisions of the Declaration of Helsinki 1995 (as revised in 2013). We observed serial paraffin sections of the body with upper extremities of 10 human embryos at 7 weeks (crown-rump length [CRL], 26-32 mm). All sections were part of the large collection kept at the Institute of Embryology, Universidad Complutense Madrid, and were products of miscarriages and ectopic pregnancies managed at the Department of Obstetrics at the university. These sections in Madrid were stained with hematoxylin and eosin (HE) or azan staining. The sectional planes were sagittal to the body and longitudinal (almost frontal) to the arm. However, because of the curved course, the humerus was not always cut longitudinally.Okajimas Folia Anat. Jpn., 93(1): 15

Teres major and latissimus dorsi muscles in human embryos: A reconsideration of the so-called brother muscles

“…A concept of brother muscles might be applied to the TM and LD according to a bias from the gross and comparative anatomy, not from the embryological view. Although the coracobrachialis and biceps short head are difficult to discriminate in embryos' arm (Yamamoto et al, 2016), they might never be called the brother muscles. Likewise, in spite of the common anlagen seen in stages much later than establishment of other flexors (Rodríguez-Vázquez et al, 2017), nobody might consider the flexor pollicis longus and flexor digitorum profundus muscles of the forearm as a pair of brothers.…”