18 Profs. D. Ferrier and G. F. Yeo. [Mar. 24, 



At present we merely note the above fact, reserving the subject for 

 future inquiry. 



The Lumbo- Sacral (Crural) Plexu's. 



The roots which supply motor fibres to the lower extremity comprise 

 the first sacral, seventh, sixth, fifth, and fourth lumbar in the monkey, 

 corresponding, as already indicated, to the second sacral, first sacral, 

 fifth, fourth, and third lumbar in man respectively. 



Stimulation of the second sacral, and of the third and fourth sacral 

 in the instance where we exposed these roots, gave rise to movements 

 of the tail. We could not determine movements of the pelvic 

 muscles. 



First Sacral (second sacral in man). — Adduction and flexion of hallux 

 (basal phalanx), flexion of the proximal phalanges of the toes with 

 slight separation and extension of the distal phalanges. The tail also 

 moves to the same side. — The action here is identical with that of 

 the first dorsal in the brachial plexus, and is due to the intrinsic 

 muscles of the foot. 



Seventh Lumbar (first sacral in man). — Flexion of the leg (ham- 

 strings), plantar flexion of the foot (sural muscles), adduction of 

 the hallux and flexion of the toes at the proximal phalanges (as in first 

 sacral) with the addition of flexion of the hallux at the distal phalanx 

 (long flexor). — The thigh is slightly rotated outwards, so that the 

 plantar aspect looks towards the middle line. 



The tibial and peroneal muscles and long flexors of the fingers do 

 not act. 



The nerves in action are branches of the great sciatic and its internal 

 popliteal divisions. 



Sixth LumJoar (fifth lumbar in man). — Rotation outwards of thigh 

 (which assumes "a position midway between extension and flexion), 

 flexion of the leg with inward rotation, so that the foot points inwards, 

 plantar flexion of the foot with flexion of the hallux and toes at their 

 distal phalanges. The outer edge of the foot is somewhat raised. — 

 This complex action involves the co-operation of many muscles difficult 

 to analyse. We noted action of muscles in the gluteal region, the 

 hamstrings, sural muscles, long flexors, the tibialis anticus and posticus, 

 the peroneal muscles, and also the extensors of the toes. 



This involves stimulation of nerves from the trunk, and from the 

 external and internal divisions of the great sciatic nerve. 



Fifth Lumbar (fourth lumbar in man). — Extension of the thigh, exten- 

 sion of the leg and pointing of great toe. — The combined result is 

 straightening of the whole limb directly backwards, and seems to be 

 the movement which immediately precedes the lifting of the foot to 

 take another step forward in the act of walking. 



