92 Journal of Comparative Neurology. 



out of about 1 1 original spino-occipital somatic motor nerves 

 in primitive craniates (3), The disappearance of the muscula- 

 ture innervated by these nerves has led to an increasing reduc- 

 tion of the somatic motor column of this region in the ascend- 

 ing series of vertebrates. Rostral to this region represented by 

 the hypoglossus, in which ventral nerves still appear in the on- 

 togeny in fishes, a number of head segments represented by the 

 branchial region have no somatic motor roots or center in cran- 

 iates. Still further rostrally, however, somatic muscles are 

 present in the form of eye muscles, and these are innervated by 

 the VI, IV and III nerves, whose nuclei of origin in the me- 

 dulla and base of the mid brain belong to the somatic motor 

 column. The region in which this column is interrupted con- 

 tains a tract of fibers, the fasciculus longitudinalis dorsalis, * 

 formed by fibers from the somatic motor column which run for 

 a short distance in this tract before going out in their nerves. 

 This somatic motor fasciculus is continued rostrally beyond the 

 nucleus of the III nerve into the thalamus, where its fibers take 

 origin from the cells of a special nucleus. The presence of this 

 nucleus and tract rostral to the first somatic motor nerve is prob- 

 ably connected with the former existence of a somatic motor 

 nerve rostral to III. This nerve would probably correspond to 

 the "anterior head cavity" of Platt. The nucleus of the 

 somatic motor fasciculus lies not far from the anterior end of 

 the brain axis in the region of the chiasma, and the center for 

 the somatic musculature would thus seem to have a greater ex- 

 tent than any of the other divisions. 



The splanchnic motor column as it enters the medulla be- 

 comes rapidly enlarged, forming the nuclei of origin of the mo- 

 tor X, IX, VII, and V nerves, supplying the musculature of 

 the branchial arches (nucleus ambiguus of the higher verte- 

 brates). It occupies the same position here as in the cord, lat- 

 teral to the ventral horn, and is distinguished from the somatic 



' I propose that this tract be known hereafter as the somatic motor fasciculus. 

 The present name indicates nothing as to its nature or function and gives only 

 an erroneous impression as to its position. It is no more longitudinal than m*ny 

 other tracts, and is in no sense dorsal, but lies ventral to the central canal. 



