362 THE AMERICAN NATURALIST. [Vor. XXXIX. 
for selachians in general, except for the connection with the 
cardinal sinus va the cloaco-rectal network. 
It is probable that the flow of blood throughout the entire 
length of the lateral vein is from the cloaco-rectal network and 
toward the precaval sinus. The steady increase in the diameter 
of the vein as it leaves the network and curves along the pelvic 
region points toward this view, as does also the presence, in the 
pelvic region of the vein, of valves placed so as to impede a 
posterior flow. The cloaco-rectal network is doubtless an indif- 
ferent region as regards flow, the blood passing from it into 
either the hepatic portal system, the cardinal system, or the 









VOTI DVLZZ 
(P p 
Fa. 7 

CU» UATROR RU 
7? 
A 


BA NON 

UN. MSI’EenE 
[ gir we» D 
ir) pnl 
SS SSS 
up OD 149 
OX) Os) 
Fic 


3. 5.— Diag ic side view of cloac tal region, showing relations of lateral veins, 
cardinal sinus, and mesenteric vein. af. cle., cloacal aperture ; arc. plv., pelvic girdle; 
gl. ri., rectal gland; z#., intestine; ms’r/., mesorectum ; ret. Vn., tworl 
cloaca and rectum; rż., rectum; s» 

- cr., cardinal sinus; sx. cr’., rectal prolongation of 
cardinal sinus; vx. 7. dx , right lateral vein; v». 7. s., left lateral vein; v». ms’en 
mesenteric vein. 
lateral veins. The blood from both the pectoral and the pelvic 
fin of one side, therefore, passes to the heart by the same vein. 
In two of the dissections made by Mr. Ulrich a suggestive 
condition was found. The lateral vein, steadily diminishing in 
caliber, was traced to the wall of the rectum where, at first 
glance, one would say that it became lost in the network. But 
close inspection revealed an extremely fine vessel which was 
virtually the continuation of the lateral vein along the side of 
the rectum. This fine vessel maintained a fairly straight course 
through the midst of the rectal network, of which, by reason of 
