Development of the Jugular Lymph Saes. 205 
which is derived, as a veno-lymphatic plexus or sac, or modified 
mammalian lymph heart, directly from the veins. Some of the 
general problems involved in the question of the early embryonic 
venous organization have been recently considered by Clark," 
Evans,'? and by Schulte and Tilney,!® while the mechanical basis 
of early embryonic vascular organization forms the subject of a 
classical monograph by Thoma.!® 
To return to the analysis of the development of the jugular 
lymph sae we therefore find that along the dorso-lateral circum- 
ference of the early pre- and posteardinal veins, in the appropriate 
stages, the redundant embryonic venous channels appear perfor- 
ated by a linear series of openings or fenestrae. At first these 
fenestre are small, but subsequently they enlarge, elongate and 
then adjacent fenestrae become confluent. 
In this manner a segment of the originally uniform pre- and 
posteardinal veins gradually becomes separated from the dorsal 
circumference of the parent vein, and forms a secondary parallel 
“‘para-precardinal” or ‘‘para-posteardinal’’ channel which, to- 
gether with the above mentioned precardinal tributaries, consti- 
tutes the anlage of the jugular lymph sac. To these venous deriva- 
tives of the precardinal tributaries and of the main channels we 
have, as above mentioned, given the name ‘‘veno-lymphatics.”’ 
One important condition develops as the result of this method 
of formation, namely, the progressive increase, up to a certain 
point, in the number of the communications which may obtain 
between the veno-lymphatic anlages of the jugular sac and the 
systemic veins. At first these communications in the precardinal 
region are represented by the terminals of the three or four dorsal 
16 Clark, Elliott R: Observations on Living Growing Lymphatics in the Tail of 
the Frog Larva. The Anatomical Record, vol. 3, 1909. 
17 vans, H. M. On the Earliest Bloodvessels in the Anterior Limb Buds of 
Birds and their Relation to the Primary Subclavian Artery. The American 
Journal of Anatomy, vol. 9, no. 2, pp. 281-319, May, 1909. 
18H. von W. Schulte and Frederick Tilney: A Note on the Organization of the 
Venous Return, with Special Reference to the Iliac Veins. The Anatomical 
Record, vol. 3, no. 11, 1909. 
19Thoma, R. Untersuchungen iiber die Histogenese und Histomechanik des 
Gefiisssystems, Stuttgart, 1893. 
