[Anatomical study of the ramification and intramuscular distribution of the intercostal nerves in man]

Minute dissection was performed on the ventral primary rami of the thoracic and the first lumbar nerves in the left half of an adult male cadaver in order to obtain more detailed data of the nerve supply to the muscles of the thorax and abdomen. The ribs, costal cartilages, sternum and vertebral column were removed to facilitate dissection. The origin, course and intramuscular distribution of the muscular branches of each nerve were examined in precise detail. The main findings are as follows: 1. The intercostal nerves The collateral branches were found in approximately 1/3 of the segments examined. Each branch rejoined the main trunk close to point in which the lateral cutaneous branch pierces through the intercostal muscles. Each lateral cutaneous branch arose from the main trunk proximal to the midaxillary line. The branch had some communications with the main trunk, and occasionally received a twig from the collateral branch. 2. The muscular branches 1) In general, the nerves to each intercostalis externus arose from the main trunk proximal to the costal angle. Additional slender twigs were occasionally found arising from the lateral cutaneous branch and joining the main supply nerve. 2) For the convenience of description of the nerve supply to the intercostalis interni et intimi, each intercostal nerve is divided into three parts from proximal to distal: part 1, the outside of the intercostalis intimus; part 2, between the intercostalis intimus and intercostalis internus; and part 3, inside the intercostalis internus. Branches to the intercostalis intimus arose in part 1, predominantly from the initial portion of the main trunk, either independently or with the branches of the intercostalis externus. In part 2, the branches generally originated as a common trunk with the branches of the intercostalis internus. 3) Branches to each subcostalis arose from the initial portion of the intercostal nerve belonging to the same intercostal space as the upper half of the muscle. The branches originated either independently or formed a common trunk with the branch to the intercostalis externus. 4) Branches to the transversus thoracis arose relatively independently from the third to sixth intercostal nerves. These branches ran inside of the nerves to the intercostalis internus and the common trunks of the intercostales internus and intimus branches, and entered the muscle from the anterior side. Each digit of the muscle was innervated by a nerve from the intercostal nerve corresponding to that costal attachment. The lower digit had an additional branch from the nerve of the upper adjoining space.(ABSTRACT TRUNCATED AT 400 WORDS)