100 H. V. NEAL 



progressive, beginning with the neck region; that they differ- 

 entiate into myotome and sclerotome; that their muscles are 

 primarily differentiated from the median wall; and that they 

 correspond numerically, as in the trunk region, with the neuro- 

 meric divisions of the neural tube. They, therefore, constitute 

 the best established evidence of the primitive metamerism of the 

 vertebrate head and of its comparability with the trunk. The 

 somitic nature of the muscles derived from them seems there- 

 fore, indisputable. 



2. Are the relations of the oculomotorius comparable with those of 

 a somatic motor spinal nerve f 



a. How is the relation of the oculomotor to the ramus profundus 

 to he interpreted? The oculomotor nerve resembles a somatic 

 motor nerve not only in its histogenesis but also in its central 

 and peripheral relations. 



Like a spinal somatic motor nerve, it arises from a nidulus 

 in the somatic motor column of a neuromeric segment of the 

 neural tube and innervates muscles derived from a somite seri- 

 ally homologous with those of the trunk. Furthermore it be- 

 comes connected with a ganglionic nerve after the manner of 

 typical spinal somatic motor nerves. 



This connection with the ramus profundus V, however, needs 

 closer scrutiny. True, it is a ganglionic nerve, but is it certain 

 that all ganglionic nerves are morphologically comparable? Our 

 present knowledge of nerve components and their differences in 

 the various cranial nerves, as demonstrated by the investigations 

 of Strong ('95), Herrick ('99) and Johnston ('05 a), discourages 

 the indiscriminate comparison of nerves on such superficial 

 grounds as the possession of a ganglion. Therefore one, who 

 maintains the similarity of the relations of the oculomotor with 

 spinal somatic motor nerves, is bound to demonstrate the mor- 

 phological similarity of the ramus ophthalmicus profundus V 

 with spinal somatic sensory nerves. That they are similar seems 

 proved first by their similar histogenesis from neural crest cells; 

 second, by their similar peripheral distribution as general cuta- 



