NERVOUS SYSTEM OF THE VERTEBRATA. 385 



tions on the topographical features of the development of the sym- 

 pathetic system in higher types are however as yet very imperfect. 



mp 



FIG. 275. TRANSVERSE SECTION TKEOUGH THE ANTERIOR PART OF THE TRUNK OF AN 

 EMBRYO OF SCYLLIUM SLIGHTLY OLDER THAN FIG. 29 B. 



The section is diagrammatic in the fact that the anterior nerve-roots have been 

 inserted for their whole length ; whereas they join the spinal cord half-way between 

 two posterior roots. 



sp.c. spinal cord ; sp.g. ganglion of posterior root ; ar. anterior root ; dn. dorsally 

 directed nerve springing from posterior root ; mp. muscle plate ; mp'. part of muscle 

 plate already converted into muscles; mp.l. part of muscle plate which gives rise to 

 the muscles of the limbs ; nl. nervus lateralis; ao. aorta ; ch. notochord; sy.g. sym- 

 pathetic ganglion ; ca.i\ cardinal vein ; sp.n. spinal nerve ; sd. segmental (archinephric) 

 duct ; at. segmental tube ; du. duodenum ; pan. pancreas ; hp.d. point of junction of 

 hepatic duct with duodenum ; umc. umbilical canal. 



B. E. II. 



25 



