HUMAN AND MAMMALIAN. 29 



fibres from the anterior bundles of the vagus and some of the hypoglossal roots, 

 especially those which turn backwards. Clarke seems to have traced a similar 

 continuity between some of the fibres of the hypoglossal and spinal accessory nerves, 

 stating that some of the fibres of the latter nerve " may be traced even to the cells 

 of the hypoglossal nucleus, where apparently they form loops of continuation with 

 the fibres of the hypoglossal nerve."^ 



If such be the truth, we have in the meduUa three classes of nerve fibres, analo- 

 gous to those I pointed out formerly as existing in the spinal cord,^ viz : — 



(1) Vagus (spinal accessory) and hypoglossal roots which arise from or terminate 

 in cells in their respective nuclei. 



(2) Vagus (spinal accessory) and hypoglossal roots meeting in cells. 



(3) Vagus (spinal accessory) and hypoglossal roots directly continuous. 



* Philos. Transactions, 1858, 252. 



" Mem. American Academy, 1851, 349. 



The three classes referred to are as follows : (1.) Anterior and posterior roots which arise from ot 

 terminate in anterior or posterior cells. (2.) Anterior and posterior roots which meet in cells near 

 the central part of the gray substance, (3.) Anterior and posterior roots which are directly con- 

 tinuous. 



