50 William F. Allen 



erably higher than the tail end. After a specimen had been satisfac- 

 torily injected it was placed in a pail of cold water till the gelatin mass 

 was hardened, and then preserved in a 4 per cent solution of formalin 

 until needed for dissection. All of the dissections were made at the 

 University of California Marine Laboratory, Pacific Grove, California. 

 The observations made from these dissections were checked up from 

 several transverse series of larva or small adult Lepisosteus, but mostly 

 from a 90 mm. L. osseus tail, which had been killed and fixed in 

 Teltyesniczky's potassium bichromate-acetic mixture, imbedded in 

 paraffin, cut 10 microns, and stained in Heidenhain's iron hsematoxylin 

 and counterstained in a concentrated alcoholic solution of orange G plus 

 a little acid fuchsin. 



Blood- AVASCULAR Supply for the Caudal Fin Eegion. 



Before taking up this most interesting system of subcutaneous vessels 

 it might be well, in order to avoid confusion, to first describe briefly the 

 distribution of the blood vessels for this region. 



The arterial trunk which supplies the caudal fin is the posterior 

 continuation of the dorsal aorta or the caudal artery (Figs. 1-3, 9-19, 

 C. A.). This trunk follows along in the haemal canal of the vertebral 

 column immediately above the caudal vein. Under the ninth from the 

 last vertebra it sends off a left caudal branch, which in company with 

 the corresponding vein passes between the superficial and deep muscles 

 of the fin to supply each. Then for a short distance the main artery 

 travels along the right side of the ninth or tenth haemal spines of the 

 tail (counting ventro-dorsad), between the vertebral column and the 

 caudal subcutaneous or lymphatic trunk to send off a branch which 

 pursues a dorso-caudal direction in company with the vertebral column; 

 while the main stem continues caudad with the caudal trunk. Before 

 the caudal fin is reached it crosses the right side of the subcutaneous 

 trunk, arriving at a position between the trunk and the ninth or tenth 

 hfemal spine of the tail, and finally when the distal end of the spine is 

 reached it makes a sharp curve at right angles to travel ventrad through 

 the basal canal of the fin. Its position in this canal is at first laterad 

 of the caudal vein and in front of the caudal trunk, but further on in 

 its ventral course it comes to lie in front of the vein. Throughout this 

 canal it sends off two caudal fin ray hranclies (Figs. 1, 2, 18 and 19, 

 C. E. A.), which run along the dorsal and ventral surfaces of each ray 

 to give "off a network for the fin meuibrane. 



