300 George 8S. Huntington and Charles F. W. McClure. 
jugular and cephalic veins (common jugular tap). This lymphati- 
co-venous connection in no way resembles those of the early veno- 
lymphatic, nor the doubtful ones in the lymphatic stages, but is 
established by a wedge shaped process of the lymph sae which is 
deeply invaginated into the angle of confluence of two veins and 
opens into the vascular lumen by a narrow slit-like aperture 
bounded by a two-lipped valve. This type of valve, also char- 
acteristic of the adult, is illustrated by figs. 4, 5, 6 and 7, which are 
photomicrographs of transverse sections through the region of the 
valve in the embryo under consideration. 
2. The subclavian approach also communicates with the ven- 
ous system at the jugulo—subelavian junction by a narrow slit- 
like aperture (jugulo-subclavian tap). 
In view of the conditions observed in the preceding stages we 
are bound to infer that these two taps have been secondarily 
formed. 
By comparing fig. 62 with fig. 3, it will be seen that the adult 
condition has been reached. 
3. The separate anlages of the thoracic duct, formed inde- 
pendently of the jugular lymph sac, have now united with each 
other, and with the dorsal process of the lymph sac above described. 
The thoracic duct, therefore, for the first time,now forms a con- 
tinuous vessel between the posterior thoracic region and the 
jugular lymph sac into which it opens dorsal to, and slightly in 
front of the tap at the common jugular confluence. In the por- 
tion of the embryo figured the thoracic duct crosses the dorsal 
surface of the subclavian artery, passes ventral to the sympa- 
thetic nerve, and from this point on to its entrance into the jugu- 
lar sac it lies between the sympathetic nerve and the thyro-cervical 
artery. Along this course it follows the dorsal surface of the left 
innominate and common jugular veins. 
4. The primitive ulnar lymphatic has lost its connection 
in this embryo with the jugular sac, as may be seen by the rela- 
tions of the sixth spinal nerve (SP.N.VIJ, fig. 62). It may be 
stated in general that the primitive ulnar lymphatic retains its 
connection with the jugular sac through the 14 mm. stage, after 
which this connection appears to be lost. This change, therefore, 
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