Development of the Jugular Lymph Saes. pa 
figs. 1,2, and 3). The latter may be double, with a larger dorsal 
and a smaller ventral connection. The embryonic arrangement 
tallies with the conditions observed in the adult, in which either 
the common jugular, or the jugulo-subclavian tap, or both, func- 
tion in individual cases as the chief portal of adult lymphatico- 
venous connection. 
After the secondary connections with the venous system have 
become established, the jugular lymphsac decreases relatively 
in size, while the systemic lymphatic channels increase propor- 
tionately in extent and complexity. In the adult, therefore, the 
jugular sac appears as a greatly reduced remnant of the extensive 
embryonic sac and serves merely as the connecting link between 
the systemic lymphatics and the venous system. In a few in- 
stances portions of the early structure become invaded by ade- 
noid growth and are thus partially transformed into lymph nodes. 
The lumen of the jugular sac is, however, even in these cases 
maintained, since it forms the channel of adult lymphatico- 
venous entry. 
The significance of the jugular lymph sae of the mammalian 
embryo and the homology existing between it and the lymph 
heart formation in lower vertebrates has been considered in a 
separate communication?® by one of the writers. 
Finally, a word concerning the relations of the thyro-cervical 
artery and the first six spinal nerves to the veno-lymphatic 
plexuses and the fully established jugular lymph sac. 
The thyro-cervical artery at first passes forward from _ its 
subclavian origin along the dorsal surface of the main venous 
channel to a point in front of the venous arch formed by the 
primitive ulnar vein as it enters the dorso-lateral circumference 
of the promontory. Here the artery turns abruptly laterad on 
to the lateral surface of the promontory where it divides into 
branches (figs. 13). In the later veno-lymphatic and lymphatic 
stages (figs. 14 to 17), the thyro-cervical artery still maintains 
°° G. 8. Huntington, ‘‘The Genetic Interpretation of the Development of the 
Mammalian Lymphatic System,’’ The Anatomical Record. Vol. 2, nos. 1 and 
2, pp.» 19-45, 1908. 
