SEGMENTAL MOTOR INNERVATION OF THE TIBIALIS ANTERIOR AND GASTROCNEMIUS-PLANTARIS MUSCLES IN THE DOG

Abstract

From an investigation of the segmental motor innervation of the anterior tibial and gastrocnemius-plantaris muscles of 14 dogs, the following facts were found: The tibialis anterior muscle in the dog received its segmental motor nerve supply from L 5, L 6 or L 7. In the majority of animals 2 roots were concerned, L 6 and L 7, with most of the fibers from L 6. Three exceptions were noted; in one, root L 5 alone was involved, in another, most of the fibers were in L 7, while in the 3d, they were almost equally distributed between L 6 and L 7. The segmental motor nerve supply of the gastrocnemius-plantaris complex arose from roots L 5, L 6, L 7 and S 1. In 9 animals 3 adjacent roots were involved. Eight of these received fibers from L 6, L 7, and S 1 while the other one involved L 5, L 6, and L 7. In 3 animals all 4 roots were involved (L 5, L 6, L 7 and S 1), and in 2 animals only 2 neighboring roots were concerned[long dash]L 6 and L 7 in one, and in the other L 7 and S 1. As a rule most of the motor fibers of the gastrocnemius-plantaris complex were carried in 2 adjacent roots, namely, L 7 and S 1. This was so in 10 animals. In two animals the majority of the fibers were supplied by L 6 and L 7, while in the remaining 2 dogs, the major portion of the fibers were carried in L 7, and the remainder of the fibers equally distributed in L 6 and S 1. The expts. show that it is necessary to transect the anterior nerve roots of L 5, L 6, L 7 and S 1 in order to insure the development of a complete paralysis of the anterior tibial and gastro-cnemium-plantaris muscles of the dog. As regards the ankle flexors and extensors of the hind leg, it is impossible to express a reliable % of total innervation that is supplied by each individual anterior nerve root.