206 



THE ELASMOBRANCH FISHES 



The supraorbital then extends forward, receiving a dorsolateral branch 

 (dl.v.), and then passes through the foramen in the roof of the olfactory 

 capsule and continues as the nasomaxillary (nm.v. ) . As this vein curves down- 

 ward within the capsule and along its posterolateral aspect it receives a fairly 

 large branch (n.v., fig. 192b), which is the result of a remarkable leash of ves- 

 sels coming from the folds of the olfactory organ. Just after the nasomaxillary 



A B 



rig. 191. Cerebral veins. (From Kex.) A. Scyllium catulus. B. Eaja asterias. 

 a.c.v., anterior cerebral vein; my., myelonal vein; p.c.v., posterior cerebral vein. 



enters the cartilage in the postero ventral region of the capsule it is joined by 

 the orbitonasal (on.v.) or anterior facial vein (a.f.v., fig. 190), which serves to 

 connect the veins under discussion wath the orbital sinus {o.s., fig. 190). The 

 nasomaxillary vein next emerges from the nasal cartilage just laterad of the 

 point where the maxillary nerve first passes under the basal fenestra (fn., 

 fig. 2, Wells, 1917) . Here it receives twigs from the skin and tissue outside of 

 the capsule, and a subrostral vessel (sr.v.) from the tip of the snout. In the 

 posterior part of its course the nasomaxillary vein swings mediad in front of 

 the superior labialis muscle (Us.) to join its mate from the opposite side to 

 form a dorsal sinus (s.) . From the sinus (s.) the buccopharyngeal veins {hp.v., 

 fig. 192b) lead backward, and at the basal angle of the cranium, right and left 

 vessels swing outward following the margin of the orbits. At the postorbital 

 process each buccopharyngeal receives one or two lateral tributaries from the 

 sides of the upper jaw, and then right and left vessels take an almost parallel 

 course posteriorly finally to empty into the anterior cardinal sinus. 



The anterior cerebral vein (a.c.v., fig. 191a) , which, as we said above, enters 

 the orbit as the principal vein from the anterior part of the brain, may vary 



