AI^ATOMT OF FISH. 



155 



an incision along the median ventral line from the level of the pec. 

 toral fins to jusl before the anus, and following the upper edge of the 

 body-cavity upward and forward cut away the body-wall, taking 

 care not to injure the Urge swimming-bladder above, nor the heart 

 in front. Now open the pericardial cavity, which lies immediately 

 behind and below the gills (see Fig. 198, Hi). Cut away the muscular 

 masses around the l)ack of the head; expose the cavity of the brain, 

 and remove the loose cellular tissae around the brain. If the gills 

 of one side are cut away and the intestine drawn out, the dissection 

 will appear very much as in Fig. 198. 



The cavity of the mouth widens rapidly, becoming behind the bran- 

 chial chamber or pharynx, whence we can pass a probe outward 



Fig. 199, — Anatomy of the brain of the Gunner, dorsal and side view. B, 01, 

 olfactory lobes ; the crura and the thalami not represented ; if, cerebral hem- 

 ispheres; (i>, optic lobes; C6, cerebellum; il/, medulla. 



through any of the gill-slits. There is a single row of sharp-pointed 

 teeth in front on both the under and upper jaws; in the pharynx 

 above and below there are rounded teeth. At the side of the pharynx 

 are the four gill-slits and the four arches. The entrance of each slit 

 is guarded in front and behind by a row of projecting tubercles 

 appended to the arches. On the outside of each arch, except the 

 fourth, is a double row of filaments, richly supplied with blood-ves- 

 sels which, shining through, give a brilliant red color to the gills; on 

 the fourth arch there is but a single row. At the upper and posterior 

 corner of the pharynx is the small opening of the short oesophagus. 

 The branchial chamber has an upward extension on the sides of 

 which lie the false gills (P«), which are accessory respiratory organs 



