370 THE AMERICAN NATURALIST. | (Vor. XXXIX. 
spaces or into any opening other than the proper one. In the 
second place, an injection mass entering by way of the renalend 
of the postcardinal vein passes directly to the great thin-walled 
cardinal sinus. No other veins can fill until the pressure in the 
cardinal sinus has increased sufficiently to force the mass on into 
the smaller and more remote spaces. This involves great dan- 
ger of bursting the wall of the cardinal sinus. In practice, the 
danger may be lessened by exerting external pressure upon the 
sinus, either with the hand or by other means, so as to prevent 
its becoming distended to its utmost capacity. 
The venous sinus is a point more favorable for injection than 
the postcardinal vein, so far as the filling of. the vessels is con- 
cerned. If the injection mass is directed backward into one arm 
of the venous sinus, the initial pressure of the fluid is exerted 
almost directly at the ends of the several main venous trunks 
which, other things being equal, stand equal chances of filling. 
In practice, however, this method has been found objectionable 
when attempted by an unskillful student (and since the fish is 
usually the first animal injected by a student in comparative 
anatomy, he is quite likely to be unskillful through lack of expe- 
rience). The venous sinus is not very favorably situated for the 
injecting operation. Great care is required lest the cannula be 
pushed against the delicate wall of the sinus so as to rupture it. 
Poor judgment in controlling the pressure on the syringe results 
in the bursting of the sinus, and often the thin-walled auricle is 
injured in the course of the operation. In the case of a prepa- 
ration for demonstration or museum purposes, the cutting of the 
venous sinus is, in itself, objectionable. 
The difficulties which are met in the injecting of the postcar- 
dinal vein or venous sinus are largely or wholly avoided by the 
use of the lateral vein. The lateral vein is a large vessel extend- 
ing along the entire length of the side wall of the abdominal 
cavity and lying just beneath the peritoneum. It is conspicuous 
in skates which have been dead not more than a day or two, 
because of the blood contained in it. It is not necessary, as in 
the case of the renal vein, to dissect out the vessel for injection. 
The following method will be found practicable. 
Open the abdominal cavity and note the position of the lateral 
