NILS ROSEN, STUDIES ON THE PLECTOGNATHS. 17 



embedded in the ventral longitudinal muscles. They receive 

 a great number of branches from the trunk-muscles. In the 

 pectoral region they tum dorsally, following for some distance 

 the anterior heads of the ventral longitudinal muscles that 

 attach to the Hgament between the clavicles. Receiving a 

 brancli from the clavicular muscles they turn caudally and 

 enter the sinus venosus, That these vessels correspond to 

 the venae laterales of the Elasmobranchs^ is from what has 

 been said above about their course, origin and entrance into 

 sinns venosus quite certain. The pointing out of the exis- 

 tence of lateral veins in a Teleost is of great interest as it 

 from the present state of our knowledge ought to be consi- 

 dered as a very primitive character, that has disappeared in 

 all other Teleosts. From this point of view the Plectognaths 

 must be given quite another place in the phylogenetical stem 

 of the Teleosts than that given by Boulenger.^ This au- 

 thor has put the Plectognaths at the top of the Teleostean 

 stock. It is, of course, perfectly impossible to think, that a 

 group of fishes that must have passed through the main 

 phylogenetical stem has preserved a character that was pre- 

 sent in the ancestors of this stem, but has disappeared in 

 all the groups that have branched off from the stem. I have, 

 however, a slight suspicion that the lateral veins are present, 

 perhaps more or less modified, even in other Teleosts, but 

 that they have hitherto been perfectly overlooked. This is, 

 of course, a question of great interest from a phylogenetical 

 point of view, and before this is settled the systematic place 

 of the Plectognaths cannot be decided. I will deal with the 

 problem of the lateral veins in a separate paper, which I 

 hope to be able to publish soon. 



Vena cardinalis posterior forms the continuation of the 

 caudal vein (v. caud.) which runs into the haemal canal. 

 The detailed course and its relation to the canal for the 

 aorta will be described in connection with the caudal verte- 

 brae. The haemal canal continues for some distance along 

 the thoracic vertebral canal and the vein leaves the canal 

 and enters into the body ca vi ty a good distance cranially to 

 the posterior wall of this cavity. At its entrance into the 

 body cavity it joins the two branches connecting it with the 



^ Not to be confused with the cutaneous lateral veins. 

 '^ Cambridge Nat. History, Vol. Fishes (1904). 



Arkiv fur zoologi. Band 7. N:o 25. 2 



