[The distribution of sensory and motor axons of the intercostal nerves and their branches (author's transl)].

As it is well established that motor axons in general display a higher acetylcholinesterase-activity than sensory axons do, the histochemical method of KARNOVSKY and ROOTS (1964) was used for the differentiation of motor and sensory fibres in the intercostal nerves and their branches. In the paravertebral sections of the intercostal nerves of the upper segments 30--35% of the nerve fibres show a high enzyme activity and therefore were classified as motoric. The percentage of the motor fibres in comparable zones of the lower segments increases to 45%. Only 15% of the nerve fibres proved to be motoric in the parasternal sections of the intercostal nerves. In a histogram of the acetylcholinesterase-positive intercostal nerve fibres 2 peaks can be seen: one in the alpha-calibre class, the second in the gamma-class. There are more motor axons in the lateral cutaneous branch of the lower intercostal nerve than in upper ones. This may be explained by the participation of these nerve branches in the innervation of the abdominal muscles. In 2 cases nerve branches of the intercostal nerve to the diaphragm were found containing 15--25% motor axons.