434 ZOOLOGY. 



from the level of the pectoral fins to just before the anus, and 

 following the upper edge of the body-cavity upward and for- 

 ward cut away the body-wall, taking care not to injure the 

 large swimming-bladder above, nor the heart in front. Now 

 open the pericardial cavity, which lies ventrally immedi- 

 ately behind the gills (see Fig. 39G, Ht}. Cut away the mus- 

 cular masses around the back of the head ; expose the cavity 

 of the brain, and remove the loose cellular tissue around the 

 nervous centres. If the gills of one side are excised and the 

 intestine drawn out, the dissection w'll appear very much as 

 in Fig. 396. 



The cavity of the mouth widens rapidly and continues as 

 the branchial chamber or pharynx (G), whence we can pass a 

 probe outward 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 inner surface of the anterior 

 three arches is smooth, while the arch behind the fourth slit 

 is much modified in shape and is armed with tubercles 

 and teeth. 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-vessels 

 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 sma'l open- 

 ing of the short oesophagus. The branchial chamber has an 

 upward extension on the sides of which lie the pseudobran- 

 chite (Ps), accessory respiratory organs not connected with 

 the gills proper, and receiving their blood-supply from distinct 

 arteries. There are no salivary glands. 



The oesophagus dilates almost immediately to form the 

 stomach (partly concealed in the figure by the liver, Li), 

 which seems hardly more than a dilatation of the intestine 

 (In}. This last is of nearly uniform size throughout, and after 

 making three or four coils terminates at the anus, immedi- 

 ately in front of the urinary and genital apertures. When 

 in situ, the terminal portion of the intestine or the rectum 



