[Morphological characteristics of the posterior brachial cutaneous nerve--a consideration of the development of cutaneous nerves in man].
The posterior brachial cutaneous nerve (Cbp) has certain characteristic features, being different from adjacent cutaneous nerves such as the medial brachial cutaneous nerve (Cbm) and the intercostobrachial nerve (Icb). These features are summarized as follows. 1) At the dorsal surface of the arm, the Cbp passes deeply beneath the fascia of the arm covering the dorsal surface of the long head of the triceps brachii, whereas the Cbm and the Icb pass superficial to it. In this area, the Cbp is accompanied in its course by a small artery. 2) The Cbp has no communication with the Cbm and the Icb on its way to the arm. 3) A precise and more detailed examination using a stereoscopic microscope reveals that the Cbp supplies the branches to the fascia of the dorsal surface of the arm, before passing through it. 4) The Cbp arises from the stem of the radial nerve forming a common trunk with the muscular branch to the long head of the triceps brachii. 5) In the brachial plexus, the Cbp is derived from segments C7 and C8, mainly the latter, and is composed of the most caudal elements of the radial nerve. According to the dermatome map, it would be unreasonable to consider that the Cbp (C8) is distributed in the skin, being intercalated between the Cbm (T1) and the Icb (T2). 6) Comparative anatomically, the Cbp cannot be observed in the monkey, dog, cat, rabbit or rat. Instead, in these animals, the muscular branch to the dorsoepitrochlearis arises from the radial nerve and takes the same course as that of the Cbp in man. According to Eisler (1901, 1912), when a muscle degenerates during the process of phylogeny or ontogeny, the supplying nerve sometimes remains in loco, as if representing the site where the muscle previously existed. As examples of these cases, Eisler described the following findings. 1) A fine branch arises from the loop of the cervical nerve and supplies the fascia, which extends between the clavicle and the omohyoid muscle. Eisler considered the fascia to be a remnant of the cleidohyoid muscle, which normally exists in lower mammals. 2) A branch sometimes arises from the lateral cutaneous branch of the upper intercostal nerve and passes along the ventral thoracic wall. Eisler considered this branch to be derived from the nerve supplying the external oblique abdominal muscle. 3) The interosseous nerve of the legs shows a remnant of the nerve supplying the pre-existing posterior interosseous muscle.(ABSTRACT TRUNCATED AT 250 WORDS)
Kasai
T
T
Chiba
S
S
Suzuki
T
T
Okuno
Y
Y
D000818:Animals; D001917:Brachial Plexus / Q000033:anatomy & histology*; D002415:Cats; D004285:Dogs; D000882:Haplorhini; D006801:Humans; D011817:Rabbits; D051381:Rats; D012867:Skin / Q000294:innervation*