474 THE DOGFISH CHAP. 



the cloaca ; the pancreas, spleen, and rectal gland ; and the 

 incomplete mesentery. Pass a seeker backwards, 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 trans- 

 versely, 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 ; the lateral cutaneous vein (Fig. 122, I.e.). 



2. The centrum and the neural and hcemal 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 (see p. 480) ; and, if 

 your section passes through a dorsal fin, the cartilaginous 

 pterygiophores and the horny fin-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 intes- 

 tine, and careful dissection 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 cceliac artery, extending downwards and backwards 

 along the stomach from above the posterior end of the 

 gullet; b, the anterior mesenteric artery, arising about 



