78 HENRY MCELDEREY KNOWER 



those of the Clarks on the development of the lymph hearts 

 of the chick ('20), but require further tests for the frog. 



THE LATER HISTORY OF THE ANTERIOR SEGMENTAL 

 AND INTERSEGMENTAL VEINS, WITH THEIR INCOR- 

 PORATION IN THE GREAT CUTANEOUS AND 

 ANTERIOR VERTEBRAL VENOUS SYSTEMS 



A brief account of the later history of the intersegmental 

 veins (especially the first three, about which questions have 

 arisen) is introduced here, with figures 37 to 40 for changes 

 in the period following the establishment of the segmental 

 blood vessels and the development of the important connec- 

 tions and functional relations described and illustrated with 

 figures 1 and 2. These blood vessel injections demonstrate 

 the continued, uninterrupted presence of the anterior inter- 

 segmental veins through all stages of their incorporation in 

 the systems of the great cutaneous and anterior vertebral 

 veins. 



The series of blood vessel injections will be also useful in 

 the study of lymphatics, since specimens from corresponding 

 larval stages have been selected to illustrate the two systems, 

 making it easy to obtain a satisfactory understanding of the 

 relations of the lymphatics to the veins in the various regions. 



The part played by the neural plexus in the origin and 

 early maintenance of the intersegmental veins, in frog larvae 

 as in other vertebrate embryos, was described in connection 

 with figure 1; and the influence of the increased supply of 

 blood through these veins from added peripheral venous loops 

 in the second period, was discussed with figure 2, as contrib- 

 uting still further to the permanence of the primary system. 



In the injection from the second period, illustrated in figure 

 37, the third intersegmental vein is demonstrated in its earli- 

 est phase, as the channel of outflow for the anterior vertebral 

 vein. Its blood being supplied from the three sources typical 

 for this vein in vertebrates from the neural plexus; from 

 the veins of the adjoining muscles ; and from the venous plexus 

 superficial to these segments it is typically a dorsolateral 



