Innervation of the scapular muscles and its morphological significance in man

The origin, course and distribution of the nerves supplying the supraspinatus, infraspinatus, subscapularis, teres minor, deltoid, teres major and latissimus dorsi were examined in 40 human body-halves. All the nerves supplying these 7 muscles derive from the brachial plexus between the upper trunk and the posterior cord. Within the plexus the nerves originate in the following order: the suprascapular nerve in the most cranial and ventral position followed caudally and dorsally the superior subscapular nerve, the axillary nerve, the inferior subscapular nerve and the thoracodorsal nerve. The superior subscapular nerve tends to innervate the upper and middle (thoracic) portions of the subscapularis. Both the axillary and inferior subscapular nerves tend to innervate the lower (axillary) portion of the subscapularis as well as the teres minor and deltoid, and the teres major, respectively. The subscapularis can be regarded as the compound muscle deriving from the components supplied by these nerves, 4 segmental nerves from C5 to C8 innervate the 7 muscles: C5, and (C6) innervate the supraspinatus; C5, and C6 the infraspinatus, the thoracic portion of the subscapularis, and the teres minor; C5, C6, and (C7) the deltoid; (C5), C6, and (C7) the axillary portion of the subscapularis; (C5), C6, and C7 the teres major; and (C6), C7, and C8 the latissimus dorsi. The relationships between the nerves and muscles suggest that these 7 muscles morphologically belong to the same group, the second group of the dorsal musculature attached to the shoulder girdle and limb. The probable process of formation of these muscles from the cervical myotoms is proposed.