SYSTEM AND SUPRARKNAL BOUIKS IN THE SPARRO^V, 



743 



the neural tube, certain ganglion cells separate themselves from 

 Its ventral border and independently migrate ventralward into 

 the neighbourhood of tlie aorta. It is these cells that form the 

 connected chain of en-ant ganglia which we know as the sympa- 

 thetic system," 



Thus in. Sparrow 16 of 6-7 somites [= 32-hr. chick] we find 

 a. well-marked neural crest, reaching from the dorsal border of 

 the spinal cord nearly to its ventral edge. PrOm the distal end 



Text- figure 1. 





mc. 



Transverse section of Sparrow 16 (6-7 somites), showing spinal cord and developia^ 

 neural crest. From the ventral end of latter cells (e) arc proliferated towards 

 the carotid artery'. 



C. Migrating cells. C.A. Carotid arterj'. JCed.C. Ependymal cell". 

 JV.C Neural crest. Ntc. Notochord. S.C. Spinal cord. 



(Sp. 16, slide 3, vow 3, section 12.> . 



of the crest, cells appear to be proliferated into the mesenchyme 

 between spinal cord and aorta (text-fig. 1). The crest at first 

 consists, in section, of a sitigle row of cells with deeply staining 

 cytoplasm and with large^ oval, lightly staining nuclei. They 

 have usually one large nucleolus, but two are sometimes present. 

 The cells of the .crest show mitotic figures especially at its ventral 

 edge. Between the latter and the dorso-lateral angle of the 



49* 



