96 PROCEEDINGS OF THE ACADEMY OF [1893. 



twenty-eight smaller lobes can be counted on the margin of the anal 

 fin. About eighteen well-marked lobes presenting the highly vas- 

 cular character of the others, already mentioned, are found to bor- 

 der the dorsal fin, the spaces between the anterior nine rays of 

 which, unlike the others of the same fins, are non-vascular. In cor- 

 respondence with this highly vascular condition of the marginal 

 lobes and the inter-radial spaces in these three sets of fins, there is 

 found to be developed a system of three sets of large arterial and 

 venous trunks which send the blood to and carry it away from the 

 vertical fins. 



The caudal termination of the caudal vein and aorta supply the 

 caudal fin. In the figure it is mainly the venous trunks which are 

 represented. It is seen that at the point where the caudal vein 

 enters the caudal fin it divides into two very large trunks, such as 

 are not met with in any other known type of fish of the same age. 

 One of these trunks passes in a dorsal and another in a ventral 

 direction, carrying away the blood from the dorsal and ventral 

 halves respectively of the caudal fin. The number of branches 

 which pass from the two trunks mentioned correspond very closely 

 to the number of inter-radial spaces. A second system of vessels, 

 much slighter in caliber after death than they probably were 

 during life, is seen just a little way anterior to the two large venous 

 trunks already described. These are probably the dorsal and ven- 

 tral branches of the arterial system into which the posterior termi- 

 nation of the caudal portion of the aorta divides in order to supply 

 the caudal fin-membranes with arterial blood. The radiating venous 

 and arterial inter-radial vessels pass quite to the margin of the 

 caudal, where they form vascular arcs around the edges of the flat 

 vascular lobes already described. From within this vascular arc to 

 the point of insertion of the caudal rays the inter-radial membrane 

 is found to be traversed by a close plexus of capillary vessels. 

 This plexus is excavated in a connective tissue which lies between 

 the epidermis of the opposite sides of the fin. 



Four sets of vascular trunks pass from the dorsal ; of these the 

 three posterior are the most strongly developed. They take their 

 rise directly from the caudal vein and caudal portion of the aorta 

 on the dorsal aspect of these vessels. Each of these vessels upon 

 reaching the base of the dorsal divides into an anterior and poste- 

 rior trunk. Each of these trunks gives off in a vertical direction 

 nearly at right angles to themselves a series of inter-radial vessels. 



