45S THE DOGFISH chap. 



roof of the skull with a knife until the brain is exposed, being caveful not 

 to injure some nerves which you will see close beneath the skin on 

 either side of the brain-case. Then cut off the tail transversely, a short 

 distance behind the pelvic fins, and on the cut surface note — 



1. The iittc;^iiincnl, in which runs the sensory canal of the lalera. 

 i;,n: 



2. The centrum and neural and lueinal arches oi the vertebra, and the 

 soft intervertel^'al substance (remains of the notochord) ; the spinal cord ; 

 and the caudal artery and vein. 



3. The myomeres and inyoconnuas : and if your section passes through 

 a dorsal On, the cartilaginous pterygiophores and the horny lin-rays. 

 Sketch. 



III. — The dor.sal aorta and its branches may now be injected (sec 

 p. 99) through the cut end of the caudal artery, into which a cannula 

 .should he inserted for some distance (tying is unnecessary). Now return 

 to the examination of the abdominal viscera, and make out : — 



1. The bile-duct, opening into the intestine just behind the pylorus. 

 The pancreatii duct runs in the wall of the intestine, and careful dis- 

 section is required to make out its course (see § IV, i). 



2. The hepatic portal vein and its factors, entering the liver near the 

 median plane. If the blood has escaped from it, try to blow it up 

 with a blowpipe. 



3. The position of the dorsal aorta, which 'will be seen better at a 

 later stage, but the chief branches of which .should now be traced to 

 their distribution, as follows : a, the caiiac artery, extending down- 

 wards and backwards along the stomach from above the posterior end 

 of the gullet ; /', the anterior mesenteric artery, arising about I^ inch 

 behind the cceliac ; c, the lieno-gastric artery, arising close behind the 

 anterior mesenteric ; and d, the small posterior mesenteric artety, pas- 

 sing downwards to the rectal gland. 



4. The large hepatic sinus, immediately in front of the liver, below 

 the gullet : slit it open, and note the veins entering it from the liver. 

 On either side of the gullet in this region, along the dor,sal surface of 

 the cceloirie, a capacious cardinal sinus will be seen : make an aperture 

 in this, and pass a seeker Ijackwards, noting that the sinus narrows into 

 the cardinal vein, which passes along the inner side of the correspond- 

 ing kidney and parallel to the aorta. T^he genital [spermatic or oz'arian) 

 sinus communicates with the cardinal. 



5. The lateral veins (Figs. 110 and 113), running (m either .side of 



