Il6 ALLEN 



noted, the sinus so designated occupies a somewhat similar po- 

 sition to the cephalic sinus of Amia, Polyodon, and Salmo. It 

 likewise receives the lateral lymphatic trunk and is connected 

 below with the pericardial sinus, but does not communicate di- 

 rectly with the jugular or the precava ; hence the term cephalic 

 sinus has been reserved for a sinus located further cephalad, that 

 corresponds in position to a similar sinus in Sco7'pcBnichthys, 

 and which terminates directly in the jugular vein. The occip- 

 ital sinus is therefore a spacious reservoir, situated directly above 

 the epibranchial of the last branchial arch, in front and a little 

 median of the pectoral arch, and immediately behind the last 

 branchial levator muscle. It also lies above and behind what 

 is represented as the branchial lymphatic sinus (Figs. 8, 9, 11 

 and 12, Br.S.)^ from which it is separated by a very thin mem- 

 brane. A little dorsad and mesad of the fourth epibranchial 

 bone there is an orifice (Figs. 8, 9, 11 and 12, Br.S.O.) in the 

 ventral wall of the occipital sinus, which communicates below 

 with the branchial sinus. Laterad and a little below the level 

 of the epibranchial of the fourth arch it is in connection with, or 

 possibly might better be represented as receiving, the pericardial 

 sinus. At this point the occipital sinus passes ventrad along the 

 inner surface of the pericardial sinus for some distance, to again 

 communicate more ventrad with the pericardial sinus (Figs. 8 

 and 10, Oc.S.O.). No special effort has been made to work 

 out in detail the distribution of the lymphatics in the pectoral 

 fin, but nevertheless in all three species of Lefisosteus a large 

 ■pectoral sinus (Figs. 8 and 9, P.S.) was found at the base of 

 each pectoral fin. With Z,. osseus it collected numerous 

 branches that traveled along the dorsal surfaces of the rays 

 and gathered a network from the adjacent membranes. Only 

 one branch per ray, however, was found in L,. osseus; whereas 

 in ScorpcBnichthys each ray possessed two vessels, which col- 

 lected a network from the adjoining membrane connecting two 

 rays. Upon reaching the anterior proximal part of the fin the 

 pectoral sinus makes a bend at right angles, and after crossing 

 diagonally over the outer surfaces of the superficial and pro- 

 fundus pectoral adductor muscles it again makes a curve at 

 right angles to pass cephalad between the profundus pectoral 



