DEVELOPMENT OF LYMPHATICS IN ANURA 67 
The primary maxillary sinus receives the lymphatic drainage 
of the head, as indicated in Hoyer’s sketches. The lymph then 
flows posteriorly towards the anterior lymph heart of the same 
side through the channel (fig. 28, lym. jug.), which has been 
mentioned as a caudal prolongation of the temporal portion of 
the sinus, though genetically it has an independent origin. Hoyer 
has called this vessel the ‘cephalic duct’ or ‘ Kopfgefiiss,’ but the 
term jugular lymphatic (lymphatica jugularis)> seems more 
appropriate on account of its probable homology with a similar 
vessel in all other vertebrates. It lies immediately dorsal to the 
pronephros (fig. 4) and only a short distance below the skin. 
Near the lymph heart a tributary is given off which extends to the 
anlage of the forelimb, at this time a knob-like condensation of 
mesenchyme beneath the operculum, and, as it is the parent 
of the future lymph vessels of the arm, this tributary may be 
called the brachial lymphatic (lymphatica brachialis). 
The relative size, shape, position, and connections of the pair 
of anterior lymph hearts during the second embryonic phase are 
exhibited in the wax reconstruction (fig. 28) and in the section 
of a 13-mm. embryo (fig. 5). Each heart is globular in form, 
placed superiorly at the posterior limit of the pronephros and is 
in continuity with both vein and lymphatic duct. It is located 
in the triangular area, bounded by skin, myotome, and the roof 
of the coelom at the level of the third spinal ganglion. On its 
ventral side it opens at the junction of the pronephric sinus and 
a short dorsal venous extension, the rudiment of the anterior 
vertebral vein of the adult. In the opposite wall of the heart the 
afferent lymphatic vessel has its entrance. 
Not only the lymphatic drainage of the head is poured into the 
anterior lymph hearts, but also the greater quantity of the lymph 
from the trunk is conveyed to them by two pairs of important 
ducts, the subvertebral lymphatics (lymphaticae subvertebrales), 
lying deep, and the lateral lymphatics (lymphaticae laterales) 
of the trunk situated superficially, one on each side. The latter 
> The usage of the word ‘lymphatic’ and its Latin form, ‘lymphatica,’ has been 
made clear in the author’s paper in The Anatomical Record, vol. 16, no. 6, August, 
1919. 
