130 



contributed to the nerves of the limb, 27,2% where eight nerves 

 contributed and 3,3 7o where nine nerves contributed. 



In Table lb is shown the frequency with which a given number 

 of spinal nerves contributed to a given type of plexus. The plexuses., 

 as will be explained in Part II in greater detail, were divided into 

 seven groups according to the most posterior spinal nerves contributing 

 to the anterior and the posterior limb nerves. In the plexuses types 

 A, B, C, D, E, the XXIV spinal (4. lumbar) nerve is the last to 

 contribute to the anterior limb nerves (femoral and obturator), in 

 types E and G the XXV spinal nerve also contributes to the anterior 

 nerves of the limb. In type A the XXVI spinal nerve is the last to 

 contribute to the posterior nerves of the limb (tibial and peroneal); 

 in type B the XXVII; in types C, D and E the XXVIII; in types F 

 and G the XXIX. In type C the supply of the XXIV nerve to the 

 sacral plexus is larger than that to the lumbar. In D the reverse 

 is true. 



The specific spinal nerves entering a given type of plexus may 

 be readily calculated from the table. Thus one instance of the plexus 

 type A was found. In this instance six spinal nerves contributed to 

 the nerves of the limb. The XXVI spinal nerve was the most posterior 

 spinal nerve to contribute to the limb nerves, the most anterior was 

 the XXI. The furcal nerve was the XXIV. The XXI to the XXIV 

 spinal nerves thus contributed to the anterior nerves of the limb and 

 the XXIV to the XXVI to the posterior. Of the plexu^s of type B 

 twenty-five instances were found in one of which a few fibres seemed 

 to be contributed from the XXIII spinal nerve to the sacral plexus. In 

 this instance the XXI to XXVII spinal nerves contributed to the nerves 

 of the limb. The XXI to the XXIV nerves contributed to the anterior, 

 the XXIII to XXVII nerves to the posterior nerves of the limb. The 

 XXI nerve contributed fibres to the lateral (external) cutaneous nerve, 

 but none to the obturator and femoral nerves. Of the other twenty- 

 four instances of type B, the XXII to the XXIV nerves contributed 

 to the anterior nerves in five instances, and the XXI to the XXIV 

 nerves in nineteen instances, in four of which no fibres were furnished 

 by the XXI nerve to the obturator and femoral nerve trunks. In all 

 24 instances the XXIV to XXVII nerves served to supply the posterior 

 nerves of the limb. 



In the same way the table indicates the number of spinal nerves 

 that contributed to the plexuses of types C, D, E, F and G. 



It will readily be noted that fewer nerves serve to supply the 

 nerves of the limb when the XXVI or XXVII spinal nerve is the 



