Some notes on the anterior dorsal fin and venous drainage in Callorhinchus (Holocephali)

The region of the anterior dorsal fin of the elephant-fish (CalZorhinchus callorhynchus (L.) has been examined by dissection, by injection of radio-opaque material and in serial sections. Particular attention has been paid to the venous system in the region. A large venous sinus lies below the basal plate of the fin skeleton and has connections running anteriorly and posteriorly in the midline. Anteriorly, the sinus is connected with the left posterior cardinal vein by a large communicating vein which lies close against the left side of the vertebral column. This arrangement is generally similar to that found in the Selachii, but in the latter group two venae circulares are found instead of the median dorsal sinus of Callorhinchus and other Holocephali.