'314 
WILLIAM F. ALLEX. 
tlie m. cordis caudalis, wliicli is some little distance beliiud 
the caudal heart, but, unlike the third ventral ramus, it inner- 
vated only the myotomes. 
The four ventral spinal nerve rami described above in 
relation to them, cordis caudalis are of considerable value as 
landmarks for studying the limits of tlie embryonic caudal 
hearts or in the adult they demonstrate that tlie m. cordis 
caudalis extends over three segments, while the caudal heart 
is somewhat shorter. 
The peculiar state of the spinal cord in the region of the 
spinal ganglion, resembling lateral ventricles of the central 
canal, and an expansion of the central canal dorsad and 
laterad in the form of rhombic lips, is reserved for a later 
paper. 
Most remarkable is the extremely rich blood supply in the 
m. cordis caudalis of the 20 cm. series. Vessels of consider- 
able size traverse long distances in this muscle, but their 
connections outside the muscle are difficult to make out. It 
can, however, be reduced to one artery and three veins if 
the caudal heart is left out. The first or most anterior vessel 
noticed in this region on the left side is an inter-segmental 
vein, consisting only of a ventral or hmmal branch which 
passes between the anterior portion of the m. cordis caudalis 
and the myotomes, dorso-cephalad, to terminate in the caudal 
vein a little in advance of the point of its bifurcation, and 
■so far as could be determined it received no branches from 
the m. cordis caudalis. The second vessel is also a vein, but 
it drains several segments and terminates in the left caudal 
heart a little anterior of its centre. To trace backward, it 
pierces the in. cordis caudalis and then continues gradually 
caudo-ventrad between the m. cordis caudalis and the 
myotomes to the posterior end of the heart, and it is this vein 
that apparently collects the blood from them, cordis caudalis. 
A little anterior of the middle of the heart a typical inter- 
segmental artery is given olf from the lateral side of the left 
caudal artery. It soon separates into dorsal and ventral 
branches, and the latter travels caudo-ventrad with the second 
