354 THE SPINAL NERVES. 



MUSCULAR DISTRIBUTION OF THE SPINAL NERVES. 



The statements made in the foregoing synopsis, and in the following lists of the 

 muscles supplied by each spinal nerve, are based mainly upon dissections and 

 pathological observations in man, but in part also upon physiological experiments in 

 the monkey. Owing to the difficulties of these investigations, and the limited 

 number of observations that have as yet been made, there is still some uncertainty 

 as to the exact supply of some of the muscles of the limbs, where the nerves 

 are mingled in plexuses before passing to their distribution, and especially as to the 

 range of individual variations. 



In the case of the short trunk-muscles, which are derived from a single 

 myomere, the nervous supply is single, coming from the nerve of that segment. In 

 more extended muscles, which are formed by the fusion of portions of several 

 segments, the nervous supply is correspondingly multiple, although there is at times 

 a reduction in the number of nerves in comparison with the segments from which 

 the muscle appears to have been derived, e.g., in the quadratus lumborum and 

 complexus. In the limbs the segmental arrangement of the muscles and nerves is 

 obscured ; but with regard to the general disposition it may be stated that most if 

 not all of the muscles are supplied from more than one spinal nerve, and that the 

 muscles on the preaxial side of the limb tend to be supplied by higher nerves than 

 those on the postaxial side. 



From the lists it will be seen that muscles of different action are often supplied 

 from the same nerve-roots. Terrier and Yeo concluded from their experiments in 

 the monkey that the muscles called into action by the stimulation of a single nerve- 

 root entering into the brachial or crural plexus form a group executing some definite 

 co-ordinated movement of the limb, but Sherrington, in numerous observations on 

 the same animal, failed to find evidence of such an association. Risien Russell, 

 while supporting Ferrier and Yeo as to the co-ordination, also points out tha^ (in 

 the dog) when antagonistic muscles are represented in the same nerve-roots, one 

 group predominates in one root and the opposite group in another root. Similarly, 

 in man, at least for the larger joints of the limbs, the muscles producing the chief 

 movements in opposite directions are mainly represented at different levels. Thus, 

 the abductors of the shoulder are innervated mainly by the fifth cervical root, and 

 the adductors by the sixth and seventh ; the flexors of the elbow are supplied mainly 

 through the fifth and sixth cervical nerves, and the extensors through the seventh and 

 eighth ; the extensors of the wrist predominate in the seventh, and the flexors in 

 the eighth cervical and first dorsal nerves. So also in the lower limb, the flexors of 

 the hip are represented mainly in the second and third lumbar nerves, and the 

 extensors in the fifth lumbar and first and second sacral ; the adductors in the third 

 and fourth lumbar, and the abductors in the fifth lumbar and first sacral nerves ; 

 the flexors of the knee in the fifth lumbar and first and second sacral nerves, and the 

 extensors in the third and fourth lumbar. 



TABLE OP THE MUSCLES SUPPLIED BY THE SEVERAL SPINAL NERVES. 



NERVE. ANTERIOR DIVISION. POSTERIOR DIVISION. 



1st cervical .-. Rectus lateralis, Rectus anticus minor and major, Rectiis posticus major and 

 Grenio-hyoid, Inf rahyoid muscles. minor, Obliquus superior 



and inferior, Complexus. 



2nd cervical . . Rectus anticus major, Longus colli, Sterno-cleido- Obliquus inferior, Com- 

 mastoid, Grenio-hyoid, Infrahyoid muscles. plexus, Splenius, Tra- 



chelo-mastoid. 



