DEVELOPMENT OF LYMPHATICS IN ANURA 69 
are a direct continuation backwards of the jugular lymphatics, 
as illustrated in figure 28, and together they possess a common 
opening into the lymph hearts. In its course caudalward, each 
lateral lymph duct runs between the myotomes and the epidermis 
(fig. 6, lym. lat.), in the lateral-line region. About halfway 
towards the posterior lymph heart, it sends off a branch which 
passes over the upper edge of the myotome to fuse with its fellow 
of the opposite side and assuming a median position (fig. 7, 
lym. dors.), proceeds distally into the tail as the dorsal lymphatic 
(lymphatica dorsalis). 
The paired subvertebral lymphatic, corresponding to the tho- 
racic ducts of the higher vertebrates, has a position along the 
aorta and dorsal to the postcardinal veins. Anteriorly, it curves 
outward under the lower margins of the myotomes to join the 
anterior end of the lateral lymph ducts in the immediate neigh- 
borhood of the anterior lymph hearts. It retains the axial loca- 
tion (fig. 6, lym. subvert.) throughout almost its entire extent and 
later becomes connected with its companion by occasional anasto- 
moses. In the vicinity of the posterior lymph heart, the duct 
again bends outward to reunite with the lateral lymph vessel of 
the same side (fig. 7). The common duct so formed later com- 
bines with the opposite one in the ventral midline and is pro- 
longed caudally into the tail as the ventral caudal lymphatic 
(lymphatica ventralis) in the base of the ventral tail fin. In 
this region, too, the iliac lymphatic (lymphatica iliaca) is given 
off to the hind limb bud. 
Fig. 6 Transverse section of a 15-mm. embryo of Bufo vulgaris through the 
trunk at the level of the 9th spinal gangha. lym. lat., lymphatica lateralis; this 
duct is plexiform in character; lym. subvert., lymphatica subvertebralis (tho- 
racic duct); 8 v. seg., 8th intersegmental vein; lat. v. card. post., lateral division 
of the posteardinal vein; the medial divisions (subeardinals) have fused to form 
the posteava which lies ventral to the aorta; mesoneph., mesonephric tubules and 
sinusoids; rect., rectum; int., intestinum; coel., coelom. 
Fig. 7 Same, at the level of the 11th spinal ganglia. X 50. cor lym. post., 
cor lymphaticum posterius; lym. dors., lymphatic dorsalis; 11 v. seg., 11th inter- 
segmental vein. Other references as in the preceding figures. Medial to the 
subvertebral lymphatics are the aorta, primary excretory ducts and the post- 
cardinal veins. 
