THE BEAIN AND SPINAL CORD. 221 



The ciliary ganglion, a derivative of the Gasserian, represents the 

 sympathetic ganglion. Ganglion cells representing a vestigial 

 posterior root may be found on the trunk of the nerve. The 

 ophthalmic division of the 5th appears to represent its posterior 

 or sensory root. 



2nd Cranial Segment. — The motor nerve is the 4th. The 

 sensory is represented by the superior maxillary division of the 

 fifth. Meckel's ganglion represents the sympathetic ganglion. 

 It is known to be derived from the same group of nerve cells as 

 the Gasserian ganglion. 



3rd Cranial Segment. — The motor nerve is the 6th and motor 

 fibres of the fifth. The sensory root is represented by the 

 inferior maxillary division of the 5th. The otic and sub- 

 maxillary represent its sympathetic ganglia. 



4th Cranial Segment. — The motor nerve is the 7th. The 

 sensory root is represented by the chorda tympani and great 

 superficial petrosal, which are developed from the geniculate 

 ganglion (Dixon). The eighth nerve and its ganglia also belong 

 to the sensory system of this segment. The great superficial 

 petrosal represents a splanchnic nerve, the chorda tympani the 

 nerve on the anterior margin of the 1st visceral cleft (see 

 p. 34). 



5th Cranial Segment. — The motor fibres of this segment have 

 probably been scattered. Some may still remain in the 9th 

 cranial nerve (glosso-pharyngeal) which is the chief nerve of the 

 segment. The ganglia on the trunk of the glosso-pharyngeal 

 represent the posterior root ganglion. The tympanic branch 

 and small superficial petrosal represent an afferent (sensory) 

 splanchnic branch. 



6th, 7th, 8th and 9th Cranial Segments. — It has been already 

 mentioned (pages 152 and 161) that the four posterior cranial seg- 

 ments are probably trunk segments which have become modified 

 and added to the head. The anterior or motor nerve roots of these 

 four segments are combined in the 12th nerve. Motor visceral 

 fibres, which issue by the anterior roots of spinal nerves, here 

 issue by the vagus and bulbar part of the spinal accessory (all 

 of which are properly designated vagal fibres — Sherrington) and 

 represent the visceral motor fibres of the four posterior cranial 

 segments. The ganglia on the root and trunk of the vagus 



