74- SUPPLEMENT ON 



several direct ramifications. But in other species this nerve is 

 altogether superficial, without communication with the spinal 

 nerve, or connected only by means of very slender threads ; 

 the second nerve of the par vagum joins a branch of the fifth 

 pair, in order to constitute the dorsal nerve. 



The last nerve of the cranium issues from the medulla 

 oblongata behind the eighth pair; after giving a branch to 

 the swimming bladder, it passes and spreads over the shoulder 

 on the muscles of the pectoral fin, and is anastomosed with the 

 first spinal nerve. The second spinal pair gives nerves to the 

 internal muscles, and to the posterior part of the same pectoral 

 fin. Those fishes whose pelvis is suspended from the humeral 

 bones, whether their ventrals be before or behind the pectorals, 

 receive the nerves allotted to them from the third and fourth 

 spinal pairs : the third supplying the muscles attached to the 

 pelvis, and the fourth principally the rays of these fins. The 

 same arrangement obtains in jugular fishes, the nerves turn- 

 ing back to the throat to attain the fins : but in abdominals, 

 the nerves supplying the ventrals, depart from pairs lower 

 down ; as for example, in carps, where they arise from the 

 seventh and eighth spinal pairs. 



Chondropterygian fishes are similarly supplied with nerves 

 from the cranium, but those of the pectorals have a greater 

 variety of origins. 



EXTERNAL ORGANS OF THE SENSES. 



The senses of smelling, seeing, and hearing, are given to 

 fishes by means of organs, analogous to those of other classes, 

 and placed in the same manner. The eye, situated in a cavity 

 of the head, as already noticed, varies in size, direction, and 

 position. In some these organs are directed towards the sky, 



