PLATE 4 
EXPLANATION OF FIGURE 
31 Reconstruction of the vascular channels and other structures in the 
region of the left pronephros in a 4-mm. embryo of Bufo vulgaris (K. E. C., series 
B 45), lateral view. X 166. 
1-4 v. seg., 1st to the 4th intersegmental veins; the beginning of the formation 
of the venous plexus in the development of the anterior lymph heart is already 
indicated by the short and irregular branches of the 3rd intersegmental vein. 
. jug. wnt., vena jugularis interna (preecardinal) 
. Jug. ext. vena jugularis externa 
. card. post., vena cardinalis externa 
d. Cuv., ductus Cuvieri 
nephst., I, II, et IIT, nephrostomes of the pronephros 
d. proneph., pronephric or primary excretory duct 
med. spin.,- medulla spinalis 
IT, I1T, IV, 2nd, 3rd and 4th spinal ganglia 
vag., a ganglionic prolongation from the vagus group back along the medulla 
oblongata; it may be a vestige associated with the lateral-line organs and later 
disappears. 
A reconstruction of the above structures in a 5-mm. embryo, representing an 
intermediate stage between that pictured on the opposite plate and that on the 
following one, was omitted with several other illustrations to reduce the cost of 
publication, although it revealed very strikingly the lymph heart plexus before 
its coalescence into a uniform cavity, a process almost completed in plate 5. 
see 
122 
