210 



frequently the number, A brief account also was given of the division 

 of the lumbo-sacral plexuses studied into various groups according 

 to the most distal spinal nerves contributing to the anterior and 

 posterior nerves of the limb. It is our purpose here to consider 

 more fully these specific groups or types of plexus. In addition to 

 treating of the origin of the main nerves of the limb from the plexus 

 a brief account will be given of the nerves which supply in part 

 those regions of the body which lie adjacent to the limb, in part the 

 skin of the limb itself. The influence of race and sex and skeletal 

 conditions on the position of the plexus is also considered. 



The specific types of Lumbo-sacral Plexus and the fre- 

 quency with which they occurred in 246 instances. 



The most frequent form of distribution of the spinal nerves to 

 the nerves of the limb is that illustrated in fig. 5 and tabulated in 

 table 5. This form of distribution occurred in 104 out of the 246 

 plexuses tabulated. 



In this type of plexus the main source of supply of the obturator 

 and femoral nerves is from the XXII, XXIII and XXIV spinal (2., 

 3. and 4. lumbar) nerves. In 78 out of the 104 plexuses the XXI 

 spinal (1. lumbar) nerve helped to supply the lateral cutaneous nerve, 

 in 28 instances it furnished a slight branch to the femoral and in 

 25 instances to the obturator. In the plexus illustrated in fig. 5 no 

 such branch was present. The main bulk of the fibres come from the 

 XXIII and XXIV spinal (3. and 4. lumbar) nerves. The 4. lumbar 

 nerve furnishes a comparatively small branch to the nerves of the 

 sacral plexus. The peroneal nerve arises from the XXIV, XXV, 

 XXVI and XXVII spinal (4. and 5. lumbar, 1. and 2. sacral) nerves. 

 Its main source of supply is from the XXV and XXVI spinal nerves. 

 The tibial nerve arises from the XXIV, XXV, XXVI, XXVII and 

 XXVIII spinal nerves. Its main source comes from the XXV, XXVI 

 and XXVII spinal nerves. The branches from the XXIV and XXVIII 

 spinal nerves are small. If we take this most frequent type of plexus 

 as the normal, we find various types of plexuses in which the spinal 

 nerves of the leg are more proximately or more distally placed in 

 relation to the vertebrae and spinal nerves. Various terms have been 

 applied to such plexuses. Eisler has classified them as "abnormar', 

 and has grouped them according to the furcal nerves (i. e., the spinal 

 nerve or nerves common to both lumbar and sacral plexuses). 

 Sherrington has called those arising from more anterior spinal nerves 

 "pre-fixed", those from more posterior, "post-fixed". We have pre- 



