HISTOGENESIS OF SYMPATHETIC SYSTEM 7 
organism except sometimes the ramus lateralis vagi.” Hooker 
(11) also observed the absence of any peripheral nervous struc- 
ture in embryos of the frog in which the entire cerebrospinal 
nervous system was extirpated early. 
Weber (’51) described a human fetus of about full term in 
which brain and spinal cord were absent, but the peripheral 
nerves, including the sympathetic nervous system, were practi- 
cally normally developed. Dart and Shellshear have interpreted 
this and other isolated cases in which peripheral nervous ele- 
ments were observed, in the absence of the cerebrospinal ner- 
vous system, as demonstrations of the mesodermal origin of 
nervous elements and the development. of the sympathetic 
nervous system independently of the neural tube. 
In the same paper in which Weber reported the human fetus 
referred to above, he also reported the case of a calf which was 
born with the absence of a portion of the spinal cord beginning at 
the fifth thoracic segment. Spinal nerves and sympathetic 
trunks were absent throughout the region in which the spinal 
cord was absent. Weber also cited two cases, one a new-born 
calf, the other a new-born pig, reported by Alesandrini (29, ’35) 
which showed conditions analogous to those observed in the 
calf reported by himself. In the light of these and similar cases 
and the results of the experimental work cited above, it must be 
obvious that in the human fetus reported by Weber and in other 
cases in which peripheral nervous elements were observed in the 
absence of the central nervous system, the latter must have 
undergone degeneration after the peripheral nervous system had 
arisen. Such cases afford no evidence of value regarding the 
origin of the sympathetic or any other part of the peripheral 
nervous system. 
Primordia of the sympathetic trunks in the absence of the 
cerebrospinal nervous system may be demonstrated experimen- 
tally. Certain embryos of the chick included in the present 
series were subjected to operation after the initial migration of 
nervous elements from the cerebrospinal nervous system had 
taken place. In these embryos, small primordia of the sym- 
pathetic trunks are present in segments in which the spinal 
