THE SYMPATHETIC NERVOUS SYSTEM IN. MAMMALS. 
185 
Explanation of Plates 22-30. 
The figures of embryonic sections are in some cases compiled from several successive 
sections, as, for example, when a nerve had to be followed for some distance. 
PLATE 22. 
Fig. 1. Transverse section of Pat embryo (5-6 days) in thoracic region. /Sp. C'., spinal 
cord; No., notochord; M.P., muscle plate; D.R., dorsal root of nerve; Al., 
alimentary canal; Ao., aorta. 
Fig. 2. Transverse section of Rabbit embryo (7 days) in thoracic region. D.G., dorsal 
ganglion and root ; Pp.N., spinal nerve; C.V., cardinal vein ; Co., coelom; 
L., lung; A.V., allantoic vein; a, somato-splanchnic angle. Other letters as 
before. 
Fig. 3. Transverse section of Mouse embryo (8 days) in lower thoracic region. 
Sp).N., S.D., I.D., superior and inferior primary divisions of spinal nerve ; H., 
heart; W.D., Wolffian duct; W.B., Wolffian body ; Sy., sympathetic cord. 
Fig. 4. Transverse section of Rat embryo (8 days) in upper thoracic region. L., 
trachea ; Art., carotid artery ; V., jugular vein ; Sy., sympathetic cord. 
PLATE 23. 
Fig. 5. T ransverse section of Rat embryo (8-9 days) in lumbar region. Sp.N., spinal 
nerve, dividing at somato-splanchnic angle (a) into somatic [So.) and splanchnic 
{Spl.) branches; Me., mesentery. 
Fig. 6. Transverse section of Mouse embryo (about 9 days) in lower thoracic region. 
Fig. 7. Transverse section of Rat embryo (about 10 days) in lumimr region. I.D., 
inferior primary division of nerve, dividing into somatic [So.) and splanchnic 
[Spl.) branches, somatic branch subdividing into dorsal or lateral (1) and 
ventral or inferior (2) branches; Sy., sympathetic cord, showing growth of 
cellular peidpheral branch [Br.). 
PLATE 24. 
Fig. 8. Transverse section of Mouse embryo in region of fore-limb. S.D., superior 
primary division, arising by two roots ; Spl., splanchnic branch of spinal nerve 
joined to sympathetic cord [Sy .); P., pleural cavity ; L., lung ; F.L., fore-limb. 
Fig. 9. Transverse section of Rat embryo (12 days) in thoracic region. 
PLATE 25. 
Fig. 10. Transverse section of Mouse embryo (about 17-18 days) in lumbar region. 
Sp.art., spinal artery; V>, vertebra (cartilaginous); Pane., pancreas; mes., 
mesentery ; K., kidney ; Spl., splanchnic branch, arising from two roots. 
MDCCCXC.—B. 2 B 
