288 George 8. Huntington and Charles F. W. McClure. 
tion between the promontory and the veno-lymphatic plexus 
correspond, approximately, to the two points at which in later 
stages the jugular lymph sac taps the venous system (see fig. 3 of 
adult). 
5. The embryo represents a stage just preceding the complete 
fusion of the dorsal and ventral plexus to form a common sac. 
6. The caudal portion of the ventral plexus has assumed a 
characteristic form which appears to precede this fusion, its 
dorsal, dilated oval portion being flexed mesad so that it les upon 
the dorsal surface of the precardinal just in front of the promon- 
tory, while its ventral, elongated segment follows the lateral sur- 
face of the promontory and precardinal, preparatory to its fusion 
with the anterior end of the dorsal plexus, which, in this case, also 
includes the cephalic division of the ventral plexus. 
7. Relation of spinal nerves to the veno-lymphatic plexus 
to be compared with relation of these nerves to the jugular lymph 
sacs of later stages and of the adult. 
8. Constant relations of thyro-cervical artery to the sub- 
clavian approach, to the veno-lymphatico-venous connection 
of the dorsal plexus at Tap C, and to the interval between the 
dorsal veno-lymphatic plexus and the caudal division of the ven- 
tral plexus. 
PRE-LYMPHATIC STAGE. 
Sracr OF EvacuaTION OF BLOOD CONTENTS OF EARLIER VENO-LYMPH- 
atic PLexus, AND APPARENT CoMPLETE TEMPORARY SEPARATION OF 
tHE Empry LympHatic Sac FROM THE PERMANENT VENOUS BLoop 
CHANNELS. 
Series 78, 12” Embryo 
Series 474, 10.7"™ Embryo, Harvard Embryological Collection 
We have already stated previously that no hard and fast lines can 
be drawn between the veno-lymphatic and definite lymphatic stages 
as far as the development of the jugular lymph sac is conncerned. 
It is convenient, however, to define certain derivatives of the 
venous system, constituting the anlages of the jugular lymph sacs, 
as ‘“‘veno-lymphaties,”’ as long as these derivations are still filled 
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