Johnston, MorpJiology of the Head. 257 



with the other brain commissures it is doubtless to be considered 

 as a part of the dorsal splanchnic decussations. 



We may summarize the dorsal commissures by saying that 

 the dorsal decussation of the cord has been differentiated in the 

 brain into separate somatic and splanchnic sensory decussations. 

 The commissura infima Halleri, the decussation between the 

 secondary vagus nuclei, the superior commissure, and the an- 

 terior commissure represent the splanchnic portion. The dorsal 

 commissure of the cerebellum, the dorsal decussation and pos- 

 terior commissure of the mesencephalon constitute the somatic 

 portion. Whether the pallial commissure will be brought into 

 the latter category on account of the relations of Locv's nerve 

 remains to be seen. 



Some reference was made to the ventral commissures in 

 discussing the morphology of the eye. The writer has nothing 

 further to add. 



18. The sympathetic sysieitt. 



The relation of the sympathetic to the four functional 

 divisions of the nervous system is important in connection with 

 the subjects dealt with in the present paper. Although the 

 sympathetic in lower vertebrates, where we must look for its 

 genetic relations, is very imperfectly understood, yet sufficient 

 is known to indicate that the sympathetic is morphologically 

 related to the visceral divisions. This is what the function of 

 the sympathetic and the central relations of its fibers in 

 higher forms has led us to expect. In the trunk regions 

 in selachians (60) the sympathetic ganglia are budded off 

 from the distal portion of the spinal ganglia after the 

 union of the ventral with the dorsal root. It does not 

 appear that anything is contributed to the sympathetic 

 by the ventral root in fishes. In the adult (64, 98) sen- 

 sory fibers coming from the viscera pass through the sym- 

 pathetic and spinal ganglia to end in the region of Clarke's 

 column in the cord, and motor fibers arising in the lateral motor 

 nucleus enter the sympathetic by way of the dorsal root (and in 

 higher forms by way of the ventral root also). If we interpret 



