ANIMALS WITH A BACKBONE. 



133 



behind and below the gills (see Fig. 139, Ht). Cut away the muscular 

 masses around the back of the head; expose the cavity of the brain, 

 and remove the loose cellular tissue 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. 139. 



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

 chial 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 entrance of each slit 

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



3"ra. 140. Anatomy of the brain of the Gunner, dorsal and side view. The ol- 

 factory lobes, the crura. and the thalami not represented. 



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 (/**), which are accessory respiratory organs 

 not connected with the gills proper, and receiving their blood supply 

 from distinct arteries. 



The oesophagus dilates almost immediately to form the stomach 

 (partly concealed in the figure by the liver, Li), which is hardly 

 thicker than the intestine (In). This last is of nearly uniform size 

 throughout; and after making three or four coils terminates at the 



