THE DEVELOPMENT OF THE CKANIAL AND SPINAL 



NERVES IN THE OCCIPITAL EEGION OF THE 



HUMAN EMBPtYO. 



BY 



GEORGE L. STREETER, M. D. 



Instructor in Anatomy, Johns Hopkins University. 

 With 4 Plates and 14 Text Figures. 



The following paper reports the results of a study of the morphology 

 of the ninth, tenth, eleventh, and twelfth cranial and the upper cervical 

 nerves, together with their ganglia, in a series of human embryos. It 

 includes a description of all the stages in the development of these 

 structures from the time at which they can first be definitely outlined 

 from the surrounding mesodermal tissue up to the time they have reached 

 adult conditions. This work was made possible through the kindness 

 of Prof. 0. Hertwig, Prof. His, and Prof. Mall, who gave the writer 

 access to their valuable embryo collections for the purposes of this study. 

 For this courtesy the writer takes advantage of the present opportunity 

 to express his appreciation. Acknowledgment is also to be made to 

 Prof. Gage, whose Buxton embryo is included in the series studied. 



The ultimate histogenesis of the nerve elements, a question which 

 has recently been thoroughly gone over by Harrison, 01, and Bardeen, 03, 

 will not be taken up. In the earliest stage where reconstruction was 

 possible the right and left divisions of the ganglion crest have migrated 

 ventro-laterally along the side of the neural tube, and are about to form 

 secondary attachments to it. Fibroblast formation is at this time well 

 under way, and peripheral fibre paths are beginning to become definite. 

 It is the consideration of the size, form, and relation of these paths and 

 the associated ganglion cell masses, in their different stages of growth, 

 toward which attention has been directed. 



The results of this study are tabulated at the end of the paper; but 

 special mention should be made of the eleventh cranial nerve. In tracing 

 out its early history it becomes more than ever apparent that it is abso- 

 lutely similar and continuous with the tenth or vagus nerve. In the 

 embryo these exist, not as two independent cranial nerves, but rather 

 as parts of a single structure, each part possessing mixed motor and 

 Americax .Touenal of Anatomy. — Vol. IV. 



