FISHES. 327 



species, indeed, it is nearly fluid. In structure, however, 

 it is nearly the same, although characterized by a few con- 

 stant marks. The subdivisions of the brain and cerebel- 

 lum, or their tubercles and lobes, are more numerous than 

 in the mammalia and birds. In one genus of fishes, the 

 Gadus, Dr M ONRO *, found spheroidal bodies between the 

 dura and pia mater, and covering the greater part of their 

 nerves, like a coat of mail, in their course towards the or- 

 gans to which they are destined. He was unable to ascer- 

 tain their use. 



The Spinal Marrow in fishes can be easily seen through 

 the large intermediate spaces of the vertical spinous pro- 

 cesses. Like the other nerves of fishes, the size of the spi- 

 nal marrow is in proportion to the size of the body, not to 

 the brain from which it proceeds. 



The external Organs of Smell present several remark- 

 able differences, according to the species, varying in num- 

 ber, shape, and position. In many fishes the nostrils are 

 single, while in others they are divided at the surface by a 

 transverse membrane, and thus exhibit the appearance of 

 being double on each side. They likewise vary in shape, 

 being round in the cod-fish, oval in the conger-eel, and ob- 

 long in others. They are placed in the snout in many 

 fishes, near the eyes in some, and between the eyes and the 

 snout in others. Where the openings are double on each 

 side, these are either placed contiguous to each other, as in 

 the carp ; at a little distance, as in the perch ; or remote, 

 as in the eel. The nostrils, in some instances, appear like 

 short tubes. 



The nasal openings are furnished with a few muscular 

 fibres, which are capable of executing a limited contractile 



Structure and Physiology of Fishes, Edin. 1785, p. 44. 



