1892.] On the Nerve-roots of the Lumbosacral Plexus. 69 



to the 6th of the clog. The chief of their conclusions, drawn from 

 examination of both limbs, are : — The majority of muscles are innerv- 

 ated by several roots. Excitation of a root determines in the muscles 

 which it supplies a total, not a partial, contraction. The tributary 

 fibres of the root are disseminated through the muscle supplied by it, 

 and not " cantonnees " in a special zone of it. Each root has a mus- 

 cular distribution almost absolutely constant in the animals of its own 

 species. The functions of analogous roots differ -very little in 

 different mammalian species. Each root supplies muscles of very 

 various, often of antagonistic, action. Excitation of a root gives a 

 combined movement, but an artificial, not a functional. The roots 

 that pass furthest into the member occupy the lowest position in the 

 cord. The innervation of the two planes of flexors and extensors is 

 not always symmetrical. The superficial layers are supplied before 

 the deep. 



Herringham,* by minute dissection of the human brachial plexus, 

 and, therefore, under disadvantage from inability to distinguish 

 clearly between afferent and efferent fibres, arrived nevertheless 

 at facts and conclusions of great importance. He found much indi- 

 vidual variation, but evidence of certain " laws." Thus : any given 

 root-fibre may alter its position relative to the vertebral column, 

 but will maintain its position relative to other fibres; of two 

 muscles, or two parts of a muscle, that which is nearer the head end 

 of the body tends to be supplied by the higher, that nearer the tail end 

 by the lower, root ; of two muscles, that nearer the long axis of the 

 body tends to be supplied by the higher, that nearer the periphery by 

 the lower, root ; of two muscles, that nearer the surface tends to be 

 supplied by the higher, that further from it by the lower, root. 



Recently Langley,t in the course of a paper on the sweat nerves 

 to the foot of the cat, refers to the movements of the limb produced 

 by excitation of roots of sciatic plexus in that animal. He desired 

 to ascertain whether the variation, which he finds considerable in the 

 distribution of the sweat nerves (sympathetic system), has a correla- 

 tive in the distribution of the nerves to the limb muscles. Like 

 Kronenberg, Eckhardt, and Peyer, he finds that the movements re- 

 sulting from stimulation of the same nerve-roots are not uniform, and 

 that the want of uniformity goes hand in hand with want of uniformity 

 in the root composition of the plexus, just such as displayed in Her- 

 ringham's dissections. 



My own observations have been made, during the past three years, 

 -chiefly on the lumbo-sacral roots of Macacus rhesus ; also on the frog, 

 rat, rabbit, cat, and dog, chiefly for the sake of comparing those 

 types with Macacus. The animals have been deeply anaesthetised 



* ' Roy. Soc. Proe.,' 1887. 



f ' JL of Physiol.,' September, 1891. 



