BLOOD-VASCULAR SYSTEM OF THE LORICATI 89 



the vagus foramen, follows along behind the nerve and receiv- 

 ing the much smaller neural vein, penetrates the anterior dorsal 

 corner of the head kidney (see fig. i6). Within the head kid- 

 ney the posterior encephalic or the most anterior neural vein 

 breaks up into very small veins, which again become collected 

 and empty into the jugular vein. 



(/;) Veins Emptying Directly into the Jugulars. — Under this 

 head belong the opercular and the 3 dorsal branchial muscle 

 veins. The latter in addition to draining the branchial muscles 

 receive also the dorsal nutrient branchial veins from the bran- 

 chial arches. In Ophiodon these veins are always present, 

 but vary considerably in their distribution. Perhaps the most 

 common arrangement is shown in fig. i. 



Opercular Veins (fig. i; Op. V.). — These veins arise on 

 the inner side of the operculars ; running dorsad behind the 

 corresponding arteries, they curve ventrad, after leaving the 

 dorsal edge of the operculars, and after receiving a branch from 

 the levator operculi muscles of Vetter, empty into the jugulars 

 a little behind the first dorsal branchial muscle veins. 



Dorsal Branchial Muscle Veins (fig. i ; Br.M.V, only the 

 second vein being lettered). — In the specimen from which fig. 

 I was drawn, the first of these vessels had its source in, and 

 received its principal supply from, the first dorsal nutrient 

 branchial vein (fig. i ; D.N.Br.V.). This vessel arises a little 

 below the dorsal bend, and is at first the most anterior of the 3 

 vessels in the dorsal part of the first branchial arch. In the 

 arch it receives a 7iutrient filament vein (fig. 2 ; N.Fil.V.), 

 coming from the inner margin of each filament. When the 

 dorsal bend of the arch is reached, the first dorsal nutrient 

 branchial vein crosses over and continues dorsad behind the 

 first efferent branchial artery. Then following along the outer 

 surface of the first obliquus dorsalis muscle from which it receives 

 a branch, it penetrates with the IX nerve through the first levator 

 arc. branch, internus muscle, and again crossing over the first 

 efferent branchial artery shortly after the carotid is given off, 

 finally empties into the ventral side of the jugular a little 

 cephalad of the opercular vein. The second dorsal branchial 

 muscle vein, in this specimen, takes its source from the union 



