10 



MOJ^PIIOLOGY OF THE 



Formation of the Tractus Solitarius. 



In carrying ont this investigation I made serial sections 

 of over fifty embrj^o rabbits. These varied in length 

 from 6 to 18 mm., and the sections from 3 to 17 /x in 

 thickness. Tliey were invariably stained with eosine and 

 cochineal. Tlie drawings are all componnd fignres, taken, 

 as the case may be, from three to perhaps twent}' of the 

 sections. They were in each case drawn witli a camera 

 hicida. 



Two embryos were chosen 10.8 mm. long, and serial 

 sections were made of each. One was cnt parallel to the 

 floor of the fonrth ventricle and the other at riolit ano-les 

 to it. I mean l)y the floor of tlie fonrth ventricle that 

 portion of it which is sitnated between tlie bend of the pons 

 Varolii and the neck-bend of the mednlla. 



A section taken from the former of these series is shown 

 in Fig. 7. The ectoderm is represented by fine dots in contra- 

 distinction to the mesoderm, in which the dots are placed far- 

 ther apart. The tissne of the Randschleier has not been drawn 

 in, bnt is represented by a space at the edge of the ectoderm, 

 next to the mesoderm. The finely drawn lines, in all 

 cases, denote nerve fibres. 



On examination of this section, we see the cavity of 

 the fonrth ventricle cnt longitndinally, nerve fibres sitnated 

 in both the Randschleier and mednllar}^ wall, and more- 

 over the Y (VII and VIII) ganglia as well as small por- 

 tions of the IX and X. The otic vesicle is also present, 

 and three separate portions of the jugnlar vein. 



If we examine closely the nerve fibres derived from each 

 ganglion, we find that there are some from the V which 



