104 Development of Occipital Nerves in Iluiuau Embryos 



The Vagus Complex includes both the vagus and accessory divisions, 

 the tenth and eleventh cranial nerves, which develop practically as a 

 single structure; though the complex is more spread out than the tri- 

 geminal, yet the relation of the accessory to the vagus is embryologically 

 much the counterpart of that of the motor root of tlie trigeminus to the 

 rest of that nerve. To speak of the two divisions as individual cranial 

 nerves is misleading; perhaps a new terminology should be introduced, 

 which would express more exactly their comparative and embryological 

 relations. Onodi, 02, has suggested the entire removal of the name 

 accessorius as an independent cranial nerve, but does not himself attempt 

 to carry it out. Eventually such a radical attack upon the nomenclature 

 may prove advisable; in this paper, however, whenever it is necessary to 

 distinguish between the different parts of the vagus complex, the original 

 usuage will be retained which is based on the gross anatomy of adult 

 specimens: the term "vagus nerve" will be applied to that portion of 

 the complex represented by the ganglion jugulare with its rootlets, and 

 the peripheral nerve trunk extending from this on which is found the 

 ganglion nodosum; the term "accessory or eleventh cranial nerve," no 

 distinction being made between vagal and spinal portions, will refer to 

 the remainder of the complex situated caudal to this, and includes gang- 

 lionated rootlets and the large motor trunk extending peripherally to the 

 sterno-cleido-mastoid and trapezius muscles. In their development it 

 will be seen that both divisions contain motor elements, which spring in 

 a continuous line from the lateral border of the neural tube as far down 

 as the third or fourth cervical segment, and sensory elements which are 

 developed from the cells of the ganglion crest. Later, following its 

 further growth, the oral or vagus division of the complex becomes pre- 

 dominantly sensory, and the caudal or accessory division predominantly 

 motor. 



The ganglion crest of the after-brain is apparently directly continuous 

 with that of the spinal cord, and extends from the first or second cervical 

 ganglion to the otic vesicle, an interruption indicating the division 

 between the ninth and tenth nerves. We agree with Dohrn, 01, who 

 describes the vagus crest as forming a unit wath the spinal crest, rather 

 than with Froriep, 01, who distinguishes between a ganglion crest of the 

 head and one of the trunk, and states that they do not simply go over 

 into one another, but overlap and run along adjacent to each other, each 

 ending for itself. Evidence of such an overlapping could not be made 

 out. 



An embryo of 4.0 mm. represents the youngest stage at which the crest 

 was sufficientlv differentiated from the mesoderm for accurate recon- 



