36 ANIMAL BIOLOGY. [Part I. 



The side of the fish that has not been dissected away should 

 be carefully skinned in order to see the distribution of two 

 of the cranial nerves. This is shown in Fig. 15. The dark 

 line is the fifth-nerve, of which one branch goes along the 



back and gives off nerve 

 branches to the dorsal fins ; 

 one branch crosses the 

 body to innervate the anal 



FIG. 15. -CRANIAL NERVES v AND x: COD. fins \ and a tnird P asses 



downwards behind the gill 

 slits to supply the pectoral and pelvic fins. The dotted line is 

 the tenth-nerve with two branches : an upper, which follows the 

 lateral line for about two-thirds of its length and then thins 

 out; a lower, which runs along the line of division between 

 the dorsal and the ventral set of muscles, and along the pos- 

 terior third of the lateral line. 



6. The Muscular System. The same Fig. (15) shows in the light 

 zigzag lines, the divisions between the myotomes or segments 

 of the body muscles. The myotomes are, however, far more 

 numerous than here figured. 



Of the skeletal and integumentary systems nothing need here 

 oe said. 



In conclusion, attention may be drawn to the following points 

 for the sake of comparison with other types : 



1. The heart has one auricle and one ventricle ; a sinus 

 venosus and a conus arteriosus. 



2. The blood after aeration is at once distributed throughout 

 the body, and is not first brought back to the heart. 



3. The kidney receives blood from the caudal vein as well as 

 from the renal arteries. 



4. There are separate apertures for the ureter, genital duct, and 

 alimentary canal. 



5. There is a common ureter for the two kidneys, which also 

 unite in the middle line. 



6. There is a common genital duct for the two testes or 

 ovaries, which also unite in the middle line. 



7. There is no connection between the kidney and the testis. 



