[The human superior posterior serratus muscle supplied by both the intercostal and dorsal scapular nerves].

A case of the superior posterior serratus muscle on the left side supplied by both the intercostal and dorsal scapular nerves was observed in a 67-year-old Japanese male cadaver at Sapporo Medical College, 1991. The innervation and intramuscular nerve distribution of this case was investigated using a binocular microscope. The belly of this muscle consisted of three parts, which were inserted into the second, third and fourth ribs, respectively (Fig. 1). The second part inserted into the third rib consisted of two offshoots, namely a medial and a lateral offshoot. The latter almost totally covered the first part inserted into the second rib. This muscle was innervated by twigs from the dorsal scapular nerve (C5) and the superficial intercostal nerves (Th1 & Th2) of Kodama (Kodama, 1986). The superficial intercostal nerve of the first thoracic segment gave off two twigs to the muscle, the superior (medial) and inferior (lateral) (Fig. 1). The intramuscular nerve distribution of this case demonstrated that, except for the lateral offshoot, the innervation of the muscle belly showed roughly segmental tendency though all of the twigs communicated with each other (Fig. 2). The lateral offshoot was chiefly innervated by the twig from the dorsal scapular nerve. It is apparent that the muscle primordium with the twig from C5, which ordinarily is situated at the cranialmost portion of the belly, instead came to rest between the first part and the medial offshoot of the second part. As a result, this muscle belly was innervated partially in a non-segmental manner.(ABSTRACT TRUNCATED AT 250 WORDS)