324 J. A. BADERTSCHER 



the right one. The anterior and central portions are cyUndrical 

 in outhne, having an almost uniform diameter. In the left 

 thymus the lumen of the anterior and central regions has entirely 

 disappeared, while in the right thymus only a trace of it persists 

 in the central portion. The caudal portion in the pericardial 

 region is greatly enlarged. The lumen in this region is broken 

 but in places is quite large in diameter. The walls are very 

 thick and irregular, no longer retaining their cylindrical shape. 



The anterior portion of the thymus also extends for a short 

 distance along the ventro-lateral aspect of the parathyroid. It 

 thus has two prongs between which lies the epithelial body. 

 This condition is not present on the right side and was not 

 observed in other specimens of about the same developmental 

 stage. In stages earlier than this the parathyroids are anterior 

 to the hypoglossal nerve. The anterior portion of the thymus 

 is in close contact with both, as shown in figure 2. In the 

 shiftings that occurred during the interval between this and the 

 previous stage it appears that a portion of the thymus was 

 carried along by the nerve and strung along the parathyroid 

 thus bringing about the split condition of its anterior end. 



Embryo of 21.5 mm. (figure 5). In this stage the vesicula 

 cervicalis has lost its connection with the ectoderm. The duc- 

 tus cervicalis has entirely disappeared. The vesicula cervicalis 

 lateralis {T.s.-V.c.l.) lies lateral to the hypoglossal nerve 

 (N.XII). It is a large fusiform shaped mass of cells containing 

 in its anterior portion a narrow tortuous lumen. This structure 

 is of a purely ectodermal origin and represents the 'thymus 

 superficialis' of Kastschenko. It is connected to the vesicula 

 cervicalis medialis by the pars intermedia or connecting band 

 (P.i.) that loops over the hypoglossal nerve. This band was 

 not observed by Kastschenko, hence he held that the superficial 

 thymus remained free from the remaining portion of the thymus. 

 The vesicula cervicalis medialis, also greatly expanded, has lost 

 its connection with the ganglion nodosum, possesses no lumen, 

 and lies along the antero-lateral side of the massive para- 

 thyroid (Pi. S) where it is fused with the anterior portion of 

 the thymus. 



