4S8 THE DOGFISH chap. 



roof of the skull with a knife until the brain is exposed, being careful 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 integument, in which runs the sensory canal of the latera. 

 Hjie. 



2. The centrum and neural and hmtnal arches of the vertebra, and the 

 soft intervertebral substance (remains of the notochord) ; the spinal cord ; 

 and the caudal artery and vein. 



3. The myomeres and myocommas ; and if your section passes through 

 a dorsal fin, the cartilaginous pterygiophores and the horny 4n-rays. 

 Sketch. 



III. — The dorsal aorta and its branches may now be injected (see 

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

 should be 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 pancreatic 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 celiac artery, extending down- 

 wards and backwards along the stomach from above the posterior end 

 of the gullet ; b, the anterior mesenteric artery, arising about \\ inch 

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

 anterior mesenteric ; and d, the small posterior mesenteric artery, 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 dorsal surface of 

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

 in this, and pass a seeker backwards, 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. The genital {spermatic or ovarian) 

 sinus communicates with the cardinal. 



5. The lateral veins (Figs, no and 113), running on either side of 



