Myotomes and Dermatomes in Man and the Distribution of Motoneurons Innervating Muscles in the Rat.

The distribution of motoneurons innervating human muscles has not been clarified, therefore many types of myotome and dermatome are used at present. We sent out a questionnaire about current myotome and dermatomes in man to 80 orthopaedic departments of universities in Japan and investigated the distribution of motoneurons innervating the muscles of the rat.From 53 replies, we found 11 types of myotome and 9 types of dermatome. Seventeen universities had no myotome facilities. The myotomes of Daniels, Jinnaka, Mayo Clinic, and Hoppenfeld were used in 9, 9, 7, 6 universities, respectively. The other myotomes are used in less than 2 universities. Two universities had no dermatome facilities. The dermatomes of Keegan-Garrett, Nozaki-Maeda, Edinger, Foerster, Chusid-McDonald, Brain, Bolk are used in 15, 10, 6, 4, 4, 4, 3 universities, respectively. The other dermatomes are used in less than 2 universities.The motoneurons innervating muscles of the rat were distributed as follows: 81% of C5 and C6 in deltoid muscle; 92% of C5 and C6 in biceps brachii muscle; 93% of C7 and C8 in triceps brachii; 85% of C7 and C8 in extensor carpi radialis; 97% of C8 and Th1 in flexor digitorum, and 91% of C8 and Th1 in flexor carpi ulnaris. The distribution of motoneurons innervating muscles of the rat was found to be similar to the current myotomes except for extensor carpi radialis.