Development of the Jugular Lymph Saes. 189 
is alone present at the common jugular angle (Common Jugular 
Tap); in fig. 1 (right side) and fig. 2. (left side), in which a com- 
munication is alone present at the jugulo-subclavian angle (Jugulo- 
Subclavian Tap) and in fig. 2 (right side) and fig. 3 (both sides) 
in which a communication is present at both of these angles. 
As will be fully deseribed in the following pages, the duplex 
character of the communication in the adult finds its explanation 
in the circumstance that the embryonic jugular lymph sac on each 
side of the body develops two caudally directed processes (Jugular 
and Subclavian Approaches), which are potentially capable of 
establishing a communication with the veins at the common jugu- 
lar and jugulo-subeclavian angles, respectively, and through which 
either one of the two or both of the typical points of communica- 
tion in the adult cat are invariably established. 
The jugular lymph sac of the embryo, which is, relatively, a 
very large structure, is in the adult much reduced in size and 
extremely variable in form. Figs. 2 (right side) and 3 (both sides) 
clearly illustrate the fact that the relations of the thyro-cervical 
artery to the jugular lymph sac are the same in the adult as in 
the embryo. This artery, a branch of the subclavian, lies ven- 
tral to the caudal end of the jugular lymph sac, both in the 
embryo and in the adult, and passes between the two typical 
points at which the jugular lymph sac communicates with the 
veins. As far as we are aware the persistence of the jugular lymph 
sac asa distinct anatomical structure in an adult mammal has not 
been hitherto recognized. 
We must also protest against the assumption that the jugular 
lymph sacs as a whole undergo subsequent transformation into 
lymph-nodes. Since they receive on the one hand the main 
systematic lymphatic trunks of the entire body, and on the other 
empty into the venous system, they necessarily maintain their 
lumen uninterrupted. In our series of 180 adult cats they 
uniformly appear as distinct, more or less well-defined sacs. 
Their walls are definite, firmer than those of the lymphatic 
vessels which empty into them, somewhat thinner than the walls 
of the veins, and often, in fully injected preparations, multilocular 
or diverticular. Exactly the same conditions are presented in 
