DISTRIBUTION OF SUBCUTANEOUS VESSELS IN GANOIDS 113 



III. DISTRIBUTION OF THE SUBCUTANEOUS VESSELS 

 IN LEPISOSTEUS. 



In this genus the subcutaneous vessels of the head, especially 

 the region adjoining the branchial arches and the heart, are far 

 more sinus-like than in Polyodon or the Selachians, and in this 

 respect they resemble the Teleosts. The so-called cephalic 

 sinus in Lepisosteus occupies a position entirely in front of the 

 branchial arches, which is far cephalad of its position in Polyo- 

 don or as set forth by Hopkins for Amia (of. cit., pp. 371-2), 

 and corresponds about to its position in Scorp&nichthys and other 

 bony fishes. Other interesting points such as a communication 

 of a so-called dorsal pericardial sinus with the inferior jugular 

 and separate dorsal and ventral branchial trunks will be de- 

 scribed at length later on in the text. Of the three species of 

 Lepisosteus that were studied no more variation could be found 

 than in different individuals of the same species. 



Longitudinal Lymphatic Trunks. With Lepisosteus as in 

 Amia and the bony fishes there are four such canals in the 

 thoracic as well as in the abdominal and caudal regions. They 

 are respectively dorsal, ventral, and lateral in position. A 

 transverse section as Fig. 16 shows that they are enveloped in a 

 mass of connective tissue, which is imbedded more or less within 

 the myotomes. To the unaided eye they appear like cavities 

 in this connective tissue. The outer walls of these vessels lie 

 directly below the skin and are frequently ruptured upon remov- 

 ing the horny exoskeleton. Except for their enormous caliber 

 and their different cephalic termination they do not differ ma- 

 terially from the similar canals of Scorpanichthys. The great 

 lateral lymphatic trunks (Figs. 8, 9, n, 12 and 16, L.L.T.) 

 upon approaching the thoracic region gradually leave the median 

 lateral line to assume a more and more dorsal position. Accom- 

 panying the ramus lateralis vagi each trunk passes beneath its 

 corresponding pectoral arch to culminate in what has been des- 

 ignated as the occipital sinus (Figs. 8, 9, n and 12, Oc.S.) 

 instead of emptying into the cephalic sinus as in Polyodon or 

 Amia. The dorsal lymphatic canal (Figs. 8, u, 12 and 16, 

 D.L. Z 1 .) travels along the median dorsal surface of the trunk, 

 and likewise has a very different ending from what Hopkins 



