A dissection of the Frog from the ventral surface to show the origins of 

 the spinal nerves and their connection with the sympathetic system. 

 The nerves are drawn black ; the dorsal aorta and its branches are 

 left white. /, the first spinal or hypoglossal nerve ; 2, the second 

 spinal or brachial nerve joined by 3, the third spinal nerve ; 4, 5, 6, 

 successive spinal nerves ; 7, S, q, three large spinal nerves uniting to 

 form Sc, the great sciatic nerve, which also receives a branch from 

 jo, the tenth spinal nerve ; Sy, the main sympathetic trunk ; Si 

 SS, successive sympathetic ganglia united to the spinal nerves by 

 communicating branches of varying length ; A V, annulus of 

 Vieussens (the loop has been drawn too large) ; Ca, calcareous 

 bodies near the exits of the spinal nerves ; Cr, the crural nerve. 



