[Anatomical study of the lumbar multifidus muscle and its innervation in human adults and fetuses].

The lumbar multifidus muscle was dissected with particular reference to its innervation in 10 Japanese adults and 10 fetuses from 5 to 10 months old. The results were as follows: 1) The multifidus muscle attached to the spinous process of a lumbar vertebra was segmentally innervated by the medial branch of the dorsal ramus of the lumbar nerve on a level with the spinous process. 2) The motor point of the nerve innervating the multifidus muscle in adults was slightly ventro-caudal to that portion of the lumbar spinous process with muscle attached. 3) The multifidus muscle in fetuses was thinner and flatter than that in adults. The motor point of the nerve innervating this muscle was slightly caudal at the lateral margin of the muscle to that portion of the lumbar spinous process with the muscle attached. These differences can be attributed to the fact that muscles used to oppose gravity are undeveloped in fetuses. 4) There was variation in 5 fascicles in total, in which the medial branch of the dorsal ramus of a lumbar nerve entered the multifidus muscle originating at the spinous process of a lower lumbar vertebra.