20 



MORPHOLOGY OF THE 



The Relation of the Oval Bundle to the Tractus Solitarius. 



The exact relation of the oval bundle to the tractus 

 solitarius is difhcult to determine. I do not in the rabl^it 

 consider them as homologous, on account of the difference 

 in their position : although portions, at least, of their fibres 

 are conthiuous with each other. 



The oval bundle is invariably found m the Rand- 



the tractus solitarius invariably 

 in the gray or mantel layer of 

 the medulla. 



In a rabbit emijryo of less 

 than 8 mm. in length, the 

 nerve fibres are not sufficiently 

 developed to allow one to follow 

 them. 



Figure 15 is a transverse 

 section of the medulla of a 

 rabbit embrvo 8 mm. in lenoth, 

 drawn under an oil immersion. 

 The nerve fibres are poorly devel- 

 oped, but can be seen leaving 

 the ganglion of the IX nerve. 

 They enter the medullary wall, 

 divide, and contribute to the 

 formation of the tractus solitarius. It will be observed that 

 this is situated within the boundary line of the mantel 

 layer, as are also a few ectodermic cells, which separate it 

 from the Randschleier. 



It is an imdoubted fact, as has alreadj' been stated, that 

 the depth of burial of the tractus solitarius depends on the 



schleier of the spinal cord ; 



Fig. 15. 



Section of the medulla of an em- 

 bryo rabbit S mm. at right angles to 

 the floor of the fourth ventricle in the 

 region of the IX ganglion, and seen 

 under an oil immersion. Gr. gray 

 layer. Rsch. Randschleier. Mes. 

 mesoderm. G. ganglion. V. lat- 

 eral root. D. dorsal root. TS. tractus 

 solitarius. 



