BLOOD-VASCULAR SYSTEM, ETC., OF AMIURUS CATUS. 431 



receives a large branch from the nasal l'egion as well as small branches 

 from the roof of the mouth. Reaching the skull it turns backwards, 

 as a large sinus-like vessel, along its side above and closely attached 

 to the branchial veins, and medial to the M. lev. branchiales, from 

 which it receives three or four small veins. 



The cavity of the skull is drained by a pair of veins which arise 

 in the nasal sac and pass inwards to unite by a transverse stem before 

 passing back along the dorso-lateral line of the wall. Usually one of 

 these veins — sometimes the right and sometimes the left — becomes 

 greatly reduced, and even disappears posteriorly to the transverse stem. 

 They again unite over the anterior end of the cerebral hemispheres, 

 and, continuing backwards, receive a number of veins and unite a 

 third time on the posterior wall, completing a second venous circle. 

 This circle receives a pair of veins from the auditory labyrinths, and 

 a median impair vein from the dorsal surface of the spinal cord. 



The veins leave the brain-case, along with the rami lateralis tri- 

 ffemini, through the supraoccipital and turn at once downward along 

 the lateral surface of its spine. As it issues from the brain-case each 

 vein receives a vessel from the dorsal musculature as far back as the 

 spine of the fourth vertebra. Again, at the transverse process of the 

 supraclavicle, it receives a vessel, which, arising in the dorsal fin, 

 descends along the anterior surface of the spine of the fourth verte- 

 bra, and runs forward above the latter. The vein then turns out- 

 wards and forwards, and enters the anterior cardinal. 



At this point the anterior cardinal turns outwards and downwards 

 upon the anterior surface of the aponeurotic membrane to join the 

 posterior cardinal immediately upon its leaving the head-kidney, and 

 from the trunvus transversus or ductus Cuvieri. The ductus runs 

 downwards and slightly forwards upon the membrane and beneath the 

 (esophagus to meet its fellow in the median line, and form with the 

 hepatic veins the sinus mrwsus. 



The vein draining the hyoidean region, called by Stannins 1 vena 

 jugularis inferior, arises in the branchiostegal rays and runs for- 

 wards along the median margin of the epi- and ceratohyals. Anteriorly 

 to the pericardial chamber the veins of both sides usually unite in 

 a single vein on the left side, surrounded by the thyroid gland, but, 

 in passing around and above the pericardial chamber, a small vein 



1 Loo. cit, p. 249. 



