118 



THE BRAIN OF FISHES 



into a somewhat flattened, transversely elongated mass, 

 showing only slight indications of a median fissure. In 

 the Shark (fig. 48) they also unite to form a large almost 

 globular mass with little trace of a median furrow. A 

 similar fasion of the two lobes occurs in some other Fishes, 

 though in the majority they exist as spheroids united only 

 by a transverse commissure. In Lepidosiren the cerebral 

 hemispheres are larger than all the rest of the brain ; 

 each of them also contains a cavity or ventricle, which is 



Fig. 54. 



Fig. 55. 



Fig. 54.— Brain of Lepidostcus or Gar-Pike. (Owen.) 7i, Olfactory ganglia; p. 

 cerebral lobes ; o, optic lobes ; c, cerebellum ; h, mednlla ; /, fourth ventricle ; U, 

 lower boundary of medulla. 



Fig. 5,5.— Brain of the Whiting. (Solly.) a. Olfactory ganglia ; b, cerebral lobes; 

 c, optic lobes ; e, cerebellum and medulla. 



prolonged into the olfactory lobe. In these respects they 

 closely agree with the cerebral lobes of Reptiles. 



In the Gar-Pike (fig. 54), the Perch, the Mackerel, and 

 many other Fishes, two additional ganglia known as the 

 Olfactory Lobes lie immediately in front of the cerebral 

 lobes, and each of them receives a long olfactory nerve. * 



■^ The Lancelot lias a single olfactory sac and a single nerve; in 

 all otlier fishes, except in the Lamprey and its allies, there are two 

 nerves (see iluxley, " Journ. of Linn. Soc." (Zool.), vol. xii. p. 224). 



