234 Journal of Comparative Neurology. 



4 — The Third Root of the Vagus. 



The third root of the vagus varies greatly in its manner of 

 origin from the medulla. It may leave the medulla by one 

 large root or by several rootlets. It receives a large compo- 

 nent from the tractus spinalis n. trigemini, a small component 

 from the fasciculus communis, and a small motor component. 

 The communis component forms the cephalic part of the root,, 

 and the motor fibers form the caudal portion. In some cases 

 these two components appear as separate rootlets. The large, 

 general cutaneous component itself may leave the brain by 

 several rootlets. The large root, thus formed, passes directly 

 laterad into the ganglionic complex, of which its ganglion forms 

 the ventral portion. As already mentioned, the ganglion of 

 the communis component probably fuses with that of the sec- 

 ond root and is comprised of neurones from the truncus viscer- 

 alis. The general cutaneous ganglion, then, forms the most 

 ventral portion of the ganglionic complex. 



The fibers which arise from the most cephalic portion of 

 the general cutaneous ganglion pass laterad through the ventral 

 part of the complex and enter the truncus glossopharyngeus. 

 They form only a small portion of the trunk, and occupy the 

 caudal part in cross section. A second cluster of fibers from 

 this ganglion ascends in the complex between the fibers of the 

 glossopharyngeus and those of the second root of the vagus, 

 and go out with the r. auricularis X. The rest of the general 

 cutaneous neurones enter the first two branchial trunks of the 

 vagus. 



The course of the motor component of this root is ob- 

 scure because of its close relation with the fourth vagus root. 

 It probably accompanies the fourth root through the ganglionic 

 complex and enters the truncus visceralis. 



5. — The Fourth Root of the Vagus. 



The fourth root of the vagus arises singly or by as many 

 as five distinct rootlets. The axones are first visible as ascend- 

 ing longitudinal fibers in the lateral column of the cord and 

 medulla. They turn abruptly laterad from this tract and 



