Jones, Development of the Sympathetic. 1 1 7 



8, Sy.^ which is the beginning of the sympathetic as an anatom- 

 ically distinct structure in this region. Scattered cells are to 

 be seen among the fibers of the first and second spinal nerves, 

 all the way up to the spinal ganglia. These cells become con- 

 tinuous below with the cells of the forming sympathetic cord. 

 Also, there is a connection between the sympathetic cord in 

 front of the second nerve and the group of cells which give rise 

 to the sympathetic in the trunk region. Tiiese facts of observa- 

 tion favor the view that the cells which enter into the formation 

 of the sympathetic cord anterior to the second spinal nerve mi- 

 grate either (a) downward from the ganglia of the first and sec- 

 ond spinal nerves or (b) forward from the structure which gives 

 rise to the sympathetic of the trunk region, posterior to the 

 second spinal nerve. However, the question of the origin of 

 these cells requires further investigation. 



(2) My preparations show that all of the sympathetic pos- 

 terior to the second spinal nerve arises from an antecedent 

 structure, which is bilaterally symmetrical, and lies closely ap- 

 plied to the dorsal and external side of the aorta, where the lat- 

 ter is double, and to the outer side of the median aorta, after 

 the union of the two trunks. This antecedent structure con- 

 sists of an irregular ridge of cells (Fig. i, Ri.) extending back 

 to the region between the ninth and tenth nerves (Fig. 7, Ri.^, 

 suffering interruption, however, in the region of the third. 

 Throughout its entire extent, this ridge is continuous inferiorly 

 with a mass of cells (Fig. i. Ma.), which, between the second 

 nerve and the anterior end of the kidney, lies between the aorta 

 and the Wolffian duct (Fig's, i, 3, 4, and 5, Ma.) and, in the 

 region of the kidney, between this organ and the aorta (Fig. 6, 

 Ma ). It extends some distance anterior to the second nerve, 

 where, however, its connection with the sympathetic is uncertain. 

 This ridge (Fig. 8, Ri.) is continuous anteriorly with the sym- 

 pathetic cord between the vagus ganglion and the second spin- 

 al nerve, and arises at the same time as this portion of the cord. 

 The division of the forming sympathetic into a portion anterior 

 to the second spinal nerve and one posterior to it is observed 

 throughout the following descriptions. 



