Development of the Jugular Lymph Saes. 193 
and is not re-established. If oneof the original connections is thus 
abandoned, it is at least evidence that both are not inviolable 
lymphatico-venous junctions which persist throughout develop- 
ment. It therefore appears quite as logical to suppose that, after 
temporary complete separation of the lymph sac, in the aberrant 
adults referred to, a secondary venous connection is established 
at only one of the two points of election, as to argue that one of the 
primitive taps persisted throughout in an unrecognizable form, 
while the other was entirely lost. 
The view that the lymphatico-venous communications of the 
adult are secondarily established in the embryo was first advanced 
by Lewis who arrived at his conclusion on the grounds that he was 
unable to determine the presence of a communication on opposite 
sides of the embryo (rabbit and pig) in the position of the adult 
openings, and that in many instances no communication could be 
detected at all. 
McClure and Silvester!® have recently shown that the plan of 
communication in the adult rabbit and pig is exactly the same as 
that in the adult cat, in that it may occur on each side of the body, 
at either one of two, or at two typical districts (common jugular 
and jugulo-subclavian angles). Therefore, while the absence of 
a symmetrical arrangement of communications on both sides of 
the embryo is no longer proof that the communications are second- 
arily established, the fact that no communications have been 
detected at all in certain stages cannot be disregarded in favoring 
this view. 
Following is a description of the relations observed by the 
writers which exist in the cat between the jugular lymph sae and 
the veins in embryos measuring over 10.5 mm. in length: 
In a 10.7 mm. embryo (Harvard Embryological Collection, 
Series 474) no communication could be observed between lymph 
sac and vein on either side except possibly at a point situated 
slightly cranial to the jugulo-subclavian junction (right side, slide 
K, section 194, and left side, slide E, sections 197-198). These 
points of communication are extremely doubtful in character but 
18 McClure and Silvester. A Comparative Study of the Lymphatico-venous 
Connections in Adult Mammals. The Anatomical Record, vol. 3, no. 10, 1909. 
THE AMERICAN JOURNAL OF ANATOMY, VOL. 10, NO. 2. 
