7(50 A. SUBBA llAU AND P. H. JOHNSON ON THE NERVOUS 



"At 144 hours the permanent ganglia appear as small clusters 

 of nerve cells, lying close to the mixed spinal nerves and con- 

 nected to them by fibrous rami covimunicantes. These ganglia 

 increase rapidly in size and are formed largely from the sympa- 

 thetic cells which have accumulated between the spinal nerves 

 and the temporary (i. e. primary) sympathetic chain. Some of 

 the cells of the temporary sympathetic chain ai-e also incorpo- 

 rated in the permanent (i. e. secondary) ganglia. Besides these 

 the permanent ganglia are formed from the cells which liave 

 migrated directly to tliem along the spinal nerves. That portion 

 of the temporary sympathetic chain which is not incorporated in 

 the ganglia of the permanent chain gradually atrophies and 

 disappears." 



Our observations therefore agree with Miss Abel's in so far as 

 they confirm the importance of the contribution from the primary 

 to tlie secondary chain. They difi'er, in assigning a definite form 

 to the accumulations of which she speaks, and in demonstrating 

 definite paths by which this contribution is eftected, i.e. the 

 dorso-lateral prolongations from the primary ganglia. More- 

 over, from the marked differentiation of the spinal nerve cells 

 from those of the sympathetic ganglia already described, we 

 question the existence of small clusters of nerve cells lying close 

 to the mixed spinal nerve, in so far as she derives them from the 

 spinal nerve directly. At the time when such clusters do occur 

 they will be found to consist of small cells with dark nuclei 

 containing many granules. We cannot see how such a meta- 

 morphosis should occur in the short passage from the dorsal 

 ganglia, all the cells of which are large, with pale nuclei and 

 containing many granules. It seems more probable that the 

 whole definitive sympathetic ganglion arises from the primary 

 sympathetic chains by migratory cells, and by active mitosis, 

 which latter can always be observed in these ganglia. 



As to the fate of the primary sympathetic, Miss Abel is in 

 accord with previous writers, all of whom express the opinion 

 that in the course of further development it atrophies and dis- 

 appears. Our material does not attain a sufliciently advanced 

 stage for us to express a definite opinion on this question, but 

 there are clear evidences of its presence in the oldest stage we 

 have observed, Sparrow 09 (= 8-day chick). The definitive 

 sympathetic chain in the cervical region of this embryo runs in 

 the vertebrarterial canal. Between the vertebne of the hinder 

 part of the neck, small bundles of fibres emerge and run ventrally, 

 but closely apposed to the cartilaginous vertebral column; these 

 fibres enter large and distinct medial ganglia, lying just under 

 the vertebral column, and above the carotids. In Sparrow B, a 

 little younger, three such medial ganglia are specially noticeable 

 (see text-fig. 11). Longitudinal fibres run from these ganglia to 

 the tissues lying between them, which are highly vascular, being 

 traversed by a capillary plexus linked up with the carotids. The 

 ultimate destiny of these ganglia awaits further investigation. 



