474 THE DOGFISH CHAP. 



and retal gland; and the incomplete mesentery. Pass a seeker back- 

 wards, on one side of the cloaca, through an abdominal pore. 



2. In the male, the spermaries, fused posteriorly ; and in the female, 

 the single ovary > and the oviducts and shell-glands. The peritoneum 

 covering the kidneys is so thick that at present they can only be 

 recognised as slightly convex ridges. 



II. Remove the skin from the dorsal surface of the head between and 

 slightly in front of and behind the eyes, and then slice away part of the 

 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 in front. 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 lateral 

 line. 



2. The centrum and neural and Juzmal 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 myocomvias ; and if your section passes through 

 a dorsal fin, the cartilaginous pterygiophores and the horny fat-rays 

 (compare Fig. in). 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 : #, the cceliac 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 cceliac ; <r, the lieno-gastric artery ', arising close behind the 

 anterior mesenteric ; and d, the small posterior mesenteric artery^ pas- 

 sing downwards to the rectal gland. 



