1/8 Journal of Comparative Neurology. 



appeared rather to arise dorsad to the fibers of the ascending 

 V and to migrate ventrad into that tract toward their exit. 

 There seems to be no representative of these fibers in "fishes," 

 nor, indeed in higher forms, unless it might be represented by 

 the ft2St-nii/us solitan'iis, a rather unsafe comparison though there 

 is a resemblance in the comparability of these with the fibers 

 of the ascending \'. The decussation of certain fibers of this 

 component in Protoptcrus, in \-icw of a similar decussation of 

 the solitary bundle observed in birds, is suggestive. The fibers 

 from the fasciculus coviuiunis are fine, with delicate m}'elin 

 sheaths, as are all fibers derived from this tract. 



X- and X^, which are verj' delicate and of few fibers each, 

 are undoubtedly motor, arising farther ventrad from the region 

 of large motor cells. 



X^ and X^ arise slightly caudad to the three rootlets above, 

 and are very close to each other. X* is probably sensory and 

 its fibers like a portion of those of X^ accompany the ascend- 

 ing \'. 



Roots X"\ X^ and undoubtedly X*^ are motor, and arise in 

 much the same manner. The root fibers of the most caudal of 

 these roots (X') may be recognized as far caudad as the caudal 

 end of the metatela, and form an ascending fasciculus in the 

 lateral columns of the oblongata adjoining the cinerea. Osborn 

 regarded this ascending bundle as the representative of the soli- 

 tar}- bundle of the mammalian brain, but erroneously, as was 

 pointed out by Strong. The entire bundle turns directly laterad 

 to constitute X". Near the exit of this root fibers appear in 

 the adjacent cinerea among the motor cells and unite to form a 

 fasciculus occupying the same position as did the fibers of X". 

 The fibers leave the brain as X" which joins X', forming the 

 major root sometimes spoken of as the eleventh nerve. In addi- 

 tion to its ascending fibers, a few entered root X' which came 

 from the region of the ascending \' and were presumably 

 sensory. In precisely the same manner as X'' arose X' which 

 was however closely related to the roots cephalad of it. 



The following Table ma\- summarize what has been said 

 above concerninsf the roots of the tenth nerve and their origin : 



