Development of the Jugular Lymph Sacs. 297 
ions of the ventral arch of the lymph sac have not united to form 
the ventral boundary of the large foramen through which the first 
and second (SP.N.J and JI) and third and fourth (SP.N.III 
and JV) spinal nerves pass on the left side (fig. 58). The fifth 
spinal nerve (SP. N.V), as on the left side, and as in all of the pre- 
ceding stages, penetrates the lymph sac. 
LYMPHATIC STAGE OR STAGE OF THE DEFINITELY ORGANIZED 
JUGULAR LYMPH SAC. 
Series 87, 14" Embryo 
Series 15, 16"”" Embryo 
Series 86, 17°" Embryo 
Series 88, 18" Embryo 
Series 22, 25"”" Embryo 
As mentioned above the jugular lymph sac consists of a single 
sac, containing no blood or only isolated corpuscles, which, after 
its apparent temporary separation from the veins in the preceding 
pre-lymphatic stage,now secondarily rejoins the venous system 
through its jugular and subclavian approaches at the common 
jugular confluence, or at the jugulo-subclavian angle, or at both 
points, depending upon the definite type of adult lymphatico- 
venous connection to be established in the individual instances. 
(See p. 188). With the assumption of this definite lymphatic 
stage the organization of the jugular sac is completed. The further 
development involves merely some topographical changes in rela- 
tion to the spinal nerves and the establishment of secondary con- 
nections with the independently formed systemic lymphatics. 
Series 87, 14°" Embryo 
Reconstruction of left side, 
Dorsal aspect, fig. 60 and 
Ventral aspect, fig. 61 
Only the caudal end of the lymph sac is shown in this recon- 
struction. 
The jugular lymph sac is much enlarged in this embryo, and the 
subcutaneous duct is still a prominent tributary of the sac. 
