132 



by us. Personal equation may play a part in this discrepancy. We 

 considered the XXVIII spinal nerve to contribute to the tibial nerve 

 in all instances where a branch from the XXVIII spinal nerve became 

 intimately connected with the tibial nerve. In such instances a few 

 bundles of fibres can always be traced well down the trunk of the 

 sciatic nerve, even though a certain percentage of the fibre bundles 

 soon leave the main nerve trunk to form one of the sources of supply 

 of the posterior cutaneous (small sciatic) nerve. The Committee for 

 Collective Examination reported (Journal of Anatomy and Physiology, 

 Vol. 29, 1885) that the last spinal nerve to supply the sciatic was 

 XXVI in one instance, XXVII in four instances and XXVIII in 

 twenty-two instances, results somewhat more nearly in accord with 

 our findings. 



Statistical treatment of the anterior limit of the lumbar plexus 

 is even more meager. The Committee for Collective Investigation 

 reported (op. cit.) that in 73 plexuses a branch from the XII thoracic 

 to the first lumbar nerve was found in forty-five instances, no such 

 branch in twenty-eight instances. Of our 246 plexuses, the XX spinal 

 nerve three times contributed fibres to the main nerves of the limb, 

 once to the lateral cutaneous only, twice to the femoral as well; the 

 XXI was the first spinal nerve to contribute fibres to the lateral 

 cutaneous nerve in 167 instances (67,8 7o) and to the femoral nerve 

 in 88 instances (35,8 ^/o), the XXII spinal nerve was the first to 

 contribute fibres to the lateral cutaneous and femoral nerves in 

 76 instances (30,9%). 



In the sacral and lumbar plexuses alike we find that the main 

 bulk of fibres going to the nerves of the limb arise from spinal nerves 

 lying between the limits of each plexus but nearer the center than 

 the extremities of the combined plexus. 



In Table 1 c is shown the relation of race, sex and side of body 

 to the plexuses in which 6., 7., 8. and 9. spinal nerves contribute to 

 the limb nerves. 



Race seems to play no very marked factor. Though the six-spinal- 

 nerve plexuses were found in a larger proportion of white than of 

 negro subjects, yet in a greater percentage of the negro subjects 

 seven-spinal-nerve plexuses were found, in a greater percentage of 

 white subjects eight-spinal-nerve plexuses and in a greater percentage 

 of negro subjects nine-spinal-nerve plexuses. 



Sex seems to play an even less noticeable factor. It is due pos- 

 sibly to chance that the eleven plexuses from white females should 

 belong to the eight-spinal-nerve form of plexus. The variations in 

 the negro males, negro females and white males are about equal. 



