96 ALLEN 



is located a little further cephalad than the similar reservoir in 

 Polyodon^ being situated entirely in front of the pectoral arch. 

 The writer observed that this sinus continued cephalad in the 

 cranium to a point about opposite the orbit. As in Polyodon it 

 is discharged into the jugular, but the orifice is said to be 

 guarded by a valve opening into the vein. No cephalic trunks 

 were represented as emptying into the cephalic sinus, but in 

 addition to the lateral trunk a fork of the dorsal is said to have 

 its termination in each. 



Cephalic lymphatic trunk (Figs, i, 2 and 3, Ceph.L.T.). 

 This is the largest and undoubtedly one of the most important 

 of the lymphatic canals in Polyodon. In a 7<>pound specimen 

 it had a length of 12 cm., extending from the base of the skull 

 to the pectoral arch, and connecting the so-called hyo-opercu- 

 laris sinus (Figs, i, 2 and 3, Hyo.O.S.} with the cephalic sinus. 

 Its caliber if anything exceeded the jugular vein, but pos- 

 teriorly it rapidly tapers down into a papilla preparatory to 

 emptying into the cephalic sinus. In position it follows along 

 directly above the jugular vein, about midway between the 

 pterotic crest and the gills. The cephalic trunk is strictly a 

 superficial canal, being separated from the branchial cavity by 

 a thick skin that bears numerous leaf-like papilla ; it is sur- 

 rounded by a tough connective tissue, and cephalad a gland-like 

 body, which I take to be the thymus, lies between it and the 

 skin. The integment of this whole region contains a typical 

 lymphatic network (Fig. i, L.N.(i)), which is collected mesad 

 by larger vessels that apparently discharge themselves into the 

 dorsal end of the hyo-opercularis sinus rather than into this 

 trunk. When the hyo-opercularis sinus is reached the cephalic 

 trunk bifurcates : the dorsal fork communicates with the hyo- 

 opercularis sinus from the rear and behind (Figs, i and 2, 

 C.L.T.O.\ while the ventral fork runs parallel, but mesad, of 

 the hyo-opercularis sinus for a short distance. In this region 

 the ventral fork receives at least two branches coming up along 

 the inner surface of the branchial levator and the pharyngo 

 clavicularis muscles. Corresponding venous trunks (Fig. i) 

 followed the course of these lymphatic branches and terminated 

 in the jugular. Frequently as is shown in Fig. i a valve is 



