133 



The side of the body probably exerts no influence on the number 

 of the spinal nerves contributing to the nerves of the limb, although 

 in this particular lot of plexuses the seven-spinal-nerve type was more 

 frequent on the right side than on the left. 



In comparing the lumbo-sacral plexus of man with that of other 

 mammals it is found that in man more spinal nerves are utilized 

 in the supply of the limb. Paterson ^) in a valuable paper on the 

 "Limb Plexuses of Mammals" says that in mammals the number of 

 spinal nerves supplying the limb nerves "is in all cases about five". 

 In man he gives the number as seven. From our tables it will be 

 seen that in man eight more frequently than seven spinal nerves 

 contribute to the supply of the limb nerves, unless we exclude from 

 the latter the lateral cutaneous nerve, in which case seven is the most 

 frequent number. In the more usual types of plexus six nerves, the 

 2., 3., 4. and 5. lumbar, and the 1. and 2. sacral nerves are the 

 spinal nerves contributing considerable branches to the limb nerves. 



Table 1. 

 Showing: a) the frequency with which a given number of spinal nerves 

 contributed to the formation of the main nerves of the limb, b) the relation of 

 this frequency to the type of plexus, and c) to race, sex and side of body in 246 

 instances. 



a. 



6 spinal nerves contributed to the main nerves of the limb in 6 instances (2,4 o/o). 



7 spinal nerves contributed to the main nerves of the limb in 66 instances (26,8 o/o), 



[In 5 instances (2 o/o of the total number) the most anterior spinal nerve giving 

 origin to the nerves of the limb supplied fibres to the lateral cutaneous nerve only.] 



8 spinal nerves contributed to the main nerves of the limb in 161 instances (65,4 o/o). 



[In 67 instances (27,2 o/o of the total number) the most anterior spinal nerve 

 giving origin to the nerves of the hmb supphed fibres to the lateral cutaneous 

 nerve only. J 



9 spinal nerves contributed to the main nerves of the limb in 13 instances (5,3 o/o). 



[In 8 instances (3,3 o/o of the total number) the most anterior spinal nerve 

 giving origin to the nerves of the limb supplied fibres to the lateral cutaneous 

 nerve only.] 



c. 

 The six plexuses in which six spinal nerves contributed to the nerves of the 

 limb were distributed as follows: 



i^egro 6 ^fgjjjale 1, left 1. 

 White 3, male 3, right side 2, left 1. 

 They constituted: 



4 o/o of the total number of plexuses (74) from white subjects. 



I) Journal of Anatomy and Physiology, Vol. 21, 1887, p. 611. 



