Development of the Jugular Lymph Saes. Zo 
1. As the result of its caudal extension, the promontory has 
become a capacious sac, involving in its caudal growth the proxi- 
mal end of the duct of Cuvier and of the posteardinal vein (see 
fig. 8). The permanent external jugular anlage now opens into 
the promontory. 
2. Precardinal dorsal tributaries 1, 2, 3 and 4 are completely 
differentiated into definite veno-lymphatic and dorsal somatic 
components. 
3. The veno-lymphatic components of precardinal tributaries 
1, 2 and 3 have become much dilated, and secondary plexus for- 
mation has now invaded the anterior portion of the straight 
segment of the precardinal. 
4. In addition to the two veno-lymphatic plexuses met with 
in the preceding group (dorsal plexus and caudal division of 
ventral plexus) the cephalic division of the ventral plexus makes 
its first definite appearance in the group under consideration. 
- Embryo 102, in spite of its smaller measurement (8.5 mm.), 
possibly due to greater curvature, offers more advanced develop- 
mental conditions than the remaining members of the group. 
It is therefore desirable to consider the last two series first. 
Series 196, 9°” Embryo 
Reconstruction of left side, 
Lateral aspect, fig. 40 
This embryo illustrates very well a condition frequently observed 
in the early stages, of comparatively advanced development of the 
veno-lymphatic area in one section, with retarded development in 
another. 
Tributary A-B forms a prominent trunk with smaller accessory 
branches (b, b’) entering the convexity of the cephalic arch caudal 
to its termination. 
Only the veno-lymphatic components of the precardinal dorsal 
tributaries 1, 2 and 3, are shown in the figure. Two prominent 
dorsal somatic tributaries open into the dorso-medial circumfer- 
ence of the precardinal in the area occupied by tributaries 1 and 
2. These lie in a line with the series of promontorial and post- 
cardinal dorsal somatic vessels and have been derived from the 
