REVIEW OF THE CRANIAL COMPONENTS. 275 



primary objects of study in this research and the teleosts 

 are too highly specialized forms to reveal to the best 

 advantage the fundamental relationships of the motor 

 centres. Nevertheless, accepting the distinction between 

 somatic motor and visceral motor nerves, as now com- 

 monly held by the morphologists, it appears that Menidia 

 conforms to the usual schema given for the vertebrates; 

 that is, the eye-muscle nerves belong to the somatic mus- 

 culature and all of the other cranial motor nerves to the 

 visceral musculature. The latter has been very highly 

 developed in the head to form the branchial musculature. 

 These muscles, to increase their physiological efficiency, 

 have become striated and the nerve fibres which supply 

 them are of large size like the other nerves for the volun- 

 tary musculature. Responding to this demand, specialized 

 centres of origin in the oblongata have appeared for these 

 nerves, viz., the nucleus ambiguus and the motor nuclei 

 of the VII and V nerves, and these nuclei are related to 

 the great longitudinal medium of muscular co-ordination, 

 the fasciculus longitudinalis dorsalis, just like the other 

 voluntary nerve centres of the somatic series. 



The well-known relations of the motor nuclei of the 

 several cranial nerves to this fasciculus are such as to 

 leave no doubt that it is physiologically a very important 

 medium of correlation of the various cranial and spinal 

 motor centres. The fact that it is related to both the 

 somatic and the visceral (branchio-motor) nuclei of origin 

 makes its morphological interpretation rather perplexing. 

 Its relations to the cranial nerve roots appear to be effected 

 mainly, at least, through the medium of collaterals. 



The findings among the motor nerves to which attention 

 is especially directed are, in addition to the preceding 

 points, the following: 



