The Motor Ganglion Cells of the Frog's Spinal Cord. 75 



In the third region several facts are noticeable: 



1. The small number of cells in proportion to the weight of 

 muscle supplied. The weight of the leg muscles is far greater 

 than that of the arm muscles, but the ganglion cells, though 

 larger are scarcely more numerous. The fibres of the muscles 

 are much larger in the leg, and of course, investigation should 

 turn on the relation of number of cells to fibres. This has 

 not been worked out. 



2. The cells increase gradually to a maximum and very 

 rapidly fall off in number at the rear end. 



3 The position of the maximum is variable and probably 

 depends on the relative size of the nerves going into the 

 lumbar plexus. This is well seen in Frog No. 43, where 

 both fibres and cells were counted. An unusually large 10th 

 nerve was found and the maximum of cells is unusually far 

 back. In general the maximum lies near the exit of the 8th 

 nerve. 



4. It may be inferred that the nerve fibres do not go far 

 in the cord before uniting with a cell. 



5. There is a long string of scattered cells at the posterior 

 end often ^ mm. long. 



The exact relation of the maxima of cells to the points of 

 exit of the nerves is not easy to determine on cross sections 

 which alone I have studied. The third nerve passes as. 

 already said, forward, and the roots of the posterior nerves 

 overlap. Longitudinal sections prepared by other meth- 

 ods will give conclusions on this point. 



A word may be said on the relation of length of cord and 

 number of cells, though no proportional relation was found. 



TABLE XVIII. 



Frog, No 



Length of cord, mm 



No. of cells 



Cells per mm 



43 



14.7 



11517 



783 



It is plain that the length increases more rapidl}^ than the 

 number of the cells. The length is necessarily taken from 



