DISTRIBUTION OF SUBCUTANEOUS VESSELS IN GANOIDS lOI 



of the facialis vein, and when the external carotid artery (Fig. 

 I, E.Car.A.) is reached, passes mesad with it in crossing 

 under the external jugular vein (Fig. i, E.J.V.\ and then 

 continues caudad a short distance, still mesad of the artery. 

 From here on, instead of passing ventrad and mesad with the 

 external carotid, it continues caudad on practically the same 

 level, directly mesad of the external jugular and above the hyo- 

 opercularis artery." In this locality, which is about opposite 

 the auditory capsule and a little above the spiracle, the facial 

 trunk collects a very rich network from the surface of the ex- 

 ternal jugular and the hyo-opercularis artery. In company 

 with the hyo-opercularis vein (Fig. \, Hyo.O.V.) this trunk 

 bends outward at right angles. In Fig. i it passes between 

 the external jugular and the hyo-opercularis artery, following 

 for a short distance below and in front of the hyo-opercularis 

 vein, and then bends at right angles, crossing under the vein 

 to terminate in the hyo-opercularis lymphatic trunk, at the point 

 where it becomes the hyo-opercularis sinus. In Fig. 2 the 

 facial lymphatic trunk after crossing under the external jugular, 

 followed below the hyo-opercularis vein for a very short dis- 

 tance, before curving, to culminate in the hyo-opercularis 

 trunk; while in Fig. 3, which is from the right side of the 

 same specimen as Fig. 2, the facial trunk after coming out 

 from under the external jugular, nearly encircles the hyo-opercu- 

 laris vein, before emptying into the hyo-opercularis trunk. 



2. Branchial Lymphatics {Nutrient Branchial Veins?). 



These vessels present the most difficult proposition found in 

 Polyodon; both in regard to tracing out their distribution, and 

 in determining whether they are veins or lymphatics, or a com- 

 mon system that may function for both. In brief, each branchial 

 arch possesses two main canals ; one of which travels along the 

 outer and inner surface of the arch ; while the other is for the 

 most part confined to the filaments, following along between the 

 two rows or hemibranchs, with the efferent branchial artery, 



1 This artery (Fig. i, Hyo.O.A.) is a large branch of the external carotid, that 

 for a short distance runs caudad with the external jugular, before bearing off 

 obliquely to the hyoidean region. 



