HANDBOOK OF PHYSIOLOGY. 



part of its dorsal portion and the upper part of its lumbar, at the origins 

 of the large nerves which, after forming the lumbar and sacral plexuses, 

 are distributed to the lower extremities. The chief cause of the greater 

 size at these parts of the spinal cord is increase in the quantity of gray 

 matter; for there seems reason to believe that the white part of the 

 cord becomes gradually and progressively larger from below upward, 

 doubtless from the addition of a certain number of upward passing 

 fibres from each pair of nerves. 



Fig. 351. From the lower lumbar cord of man, after a preparation by Klonne and Miiller, of 

 Berlin (No. 11,153), stained by Weigert and PaPs method. A portion of the gray substance of the 

 ventral cornu with the adjoining portions of theH ate ral column is represented, showing anterior 

 horn cells and the fine medullated fibres which enter the gray substance from the lateral column 

 and surround the nerve-cells, which here are provided with fine pigmented granules. High power. 

 (Koelliker.) 



From careful estimates of the number of nerve-fibres in a transverse 

 section of the cord toward its upper end, and the number entering or 

 issuing from it by the anterior and posterior roots of each pair of nerves, 

 it has been shown that in the human spinal cord not more than half 

 of the total number of nerve-fibres of all the spinal nerves are contained 

 in a transverse section near its upper end. It is obvious, therefore, that 

 at least half of the nerve-fibres entering it must terminate somewhere in 

 the cord itself. 



