PLATE 1 



EXPLANATION OF FIGURES 



13 Human embryo, 7 mm. in length, (317 — 13 — 1 — 3X315. Transverse section 

 through lower thoracic region showing spinal nerve and sympathetic trunk. 

 a, aorta; c, communicating ramus; sp, spinal nerve; Sy, sympathetic trunk. 



14 Human embryo, 9 mm. in length, 721 — 13 — 1 — 3X335. Transverse section 

 showing ventral root of spinal nerve with migrant medullary cells icvr). 



15 Human embryo, 14 mm. in length, 511 — 9 — 1—2X160. Sagittal section 

 showing vagus branch to bulbar region of. heart with aggregates of cells which 

 become incorporated in cardiac plexus (cp). 



216 



