227 



be placed were obtained in but fifty-seven instances in connection with 

 the plexuses tabulated in these tables. So far as can be judged from 

 these few instances the position of the lumbo-sacral plexus in relation 

 to the spinal nerves has no specific influence in determining the 

 cutaneous distributions of the dorsal divisions of the spinal nerves. 

 Most commonly the XXII spinal (2. lumbar) nerve is the most distal 

 spinal to furnish one of these branches. In the proximal type of 

 plexus B (fig. 3 and table 3) the XXIII and XXIV lumbar nerves 

 occupied this position more commonly than the XXI and XXII so 

 that here more distal spinal nerves than usual were distributed 

 over the buttock. 



In type C (fig. 4 and table 4) the XXII spinal nerve served 

 this function with about the same frequency as the XXIII, in type D 

 much more frequently. In types F and G, however, the more distal 

 spinal nerves furnished cutaneous branches. 



Satisfactory records were not obtained of the dorsal cutaneous 

 nerves supply arising from the sacral and coccygeal nerves. 



Explanation of Tables 2 — 8. 



These tables are arranged to show the relation of the main nerves arising 

 from the lumbo-sacral plexus to the spinal nerves which enter into the formation 

 of the plexus. Each taole corresponds to a given type of plexus. The plexuses 

 are grouped into various types according to the most distal spinal nerves which 

 contributed to the main nerves of the limb. In type A the XXVI spinal nerve 

 is the most distal nerve contributing to the main nerves of the limb; in type B 

 the XXVII, in type C, D and E the XXVIII. In type C the greater part of 

 the fibres of the XXIV spinal nerve are given to the posterior nerves of the limb; 

 in type D and E to the anterior nerves. In type E the XXV spinal nerve 

 contributes to the anterior nerves of the Umb. In types F and G the XXIX 

 spinal nerve is the last to contribute to the main nerves of the limb. In type G 

 the XXV spinal nerve contributes to the anterior nerves of the limb. 



In the column at the left in the tables the spinal nerves are indicated by 

 Koman numerals. The nerves arising from these spinal nerves are arranged in a 

 horizontal series. Under each of these nerves is indicated the number of times 

 which a given spinal nerve contributed to the supply of a given peripheral nerve 

 in the total number of plexus of a given type. Thus the last spinal nerve to the 

 rectus abdominis muscle arose from the XIX spinal nerve in ten (40 7o) and 

 from the XX in fifteen (.60 %) oi the total number of instances of type B. In 

 case the supply of a given spinal nerve to a peripheral nerve is not a direct one, 

 but is through a proximal communicating branch to the spinal nerve from which 

 peripheral nerve arises, this proximal communicating branch is indicated by (C). 

 Thus imder type B the XX spinal nerve gave rise directly to the iliac nerve in 

 seventeen instances and in two instances it contributed indirectly to it, through a 

 proximal communicating branch to the XXI. Parentheses indicate that the branch 

 supplied was small. Thus in the type B the XXIV spinal nerve contributed a 

 small branch to the femoral nerve in twenty instances and the larger part of its 

 bulk in five. 



The tables for the rest are self explanatory. 



15' 



