328 J. A. BADERTSCHER 



secondary lobulation the lobes of which on account of their 

 large size lie in general more closely together than those in the 

 previous stage. The parathyroid lies partly imbedded in the 

 dorso-mesial aspect of the thymus head slightly anterior to its 

 central portion. The superficial thymus lies closely along the 

 antero-lateral aspect of the thymus head but is not fused to it. 



Embryo of 63 mm. The connecting band on both the right 

 and left sides loops over the hypoglossal nerve. They are com- 

 paratively large and have an irregular surface similar to the 

 left connecting band in the preceding stage. Aside from their 

 greater size the large segments of the thymus in this stage present 

 no striking morphological changes from those of the 52 mm. 

 embryo. 



Embryo of 95 mm. {figures 6 and 7). This is the oldest stage 

 in which the anterior portion of the thymus was modelled. The 

 left thymus was chosen for reconstruction although the right 

 one would have done equally well. Figure 6 represents a lateral 

 aspect of the thymus head {C.t.) and the superficial thymus 

 (T.s.) The thymus head lies alongside the common carotid 

 artery (A.c), its anterior end lying near the bifurcation into the 

 external and internal carotid arteries. The parathyroid {Pt. 3) 

 lies about midway between the two ends of the thymus head 

 along its dorsal border and is closely attached to it. The super- 

 ficial thymus {T.s) lies along the anterior half of the lateral 

 aspect of the thymus head. Its dorsal and ventral borders are 

 almost parallel to each other. The caudal border is rounding 

 while its anterior part tapers irregularly into the slender connect- 

 ing band {P.i.) which loops over the hypoglossal nerve {N.XII) 

 and is connected with the thymus head. Figure 7 represents a 

 ventral aspect of the same structures as seen in figure 6. The 

 superficial thymus {T.s.) and the thymus head {C.t.) are flat- 

 tened laterally. The anterior portion of the thymus head lies 

 in contact with the dorsal border of the hypoglossal nerve. The 

 superficial thymus lies closely against the thymus head but is 

 not fused with it. Its posterior border on the right side gradu- 

 ally tapers down to a thin edge in contrast to the blunt posterior 

 border of the left superficial thymus. The diameter of the inter- 



