762 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [16] ! 



nerve. Such a thing as the brauches of nerves eventually becoming 

 new and independent nerves does occur in fishes, and I would invite 

 attention to the condition seen in the spinal nerves in the Gadidse,^ and 

 to the condition seen in the ramus palatinus nervi facialis in many \ 

 bony fishes. There are two factors to be taken into consideration that 

 enter into such a divisional process. The first of these is that distal 

 regions supplied by the nerve may grow apart, and become further and 

 further separated from each other ; and the second is, that the tendency 

 of each nerve is to take a direct course to the part it supplies. Both of 

 these conditions would eventually bring about a division of a nerve to its 

 very origin. Therefore this division must begin at the distal end of the 

 nerve, and, gradually progressing, must extend finally to the point of 

 origin in the central nervous system. 



Precisely the opposite condition is found in the first occipital nerve; 

 distally it is united with the second occipital nerve, it being but par- 1 

 tially separated from it. Therefore the only justifiable conclusion we 

 have left us to adopt is that this nerve must be considered as a discrete 

 spinal nerve, the survivor of a retrogressive process, and so in Amia 

 we must assume that at least three vertebrae have merged into the 

 cranium. 



I have yet to invite more careful attention to a condition not remarked 

 upon by me before. Upon closer scrutiny of the occipitale laterale one 

 sees that the hinder most part of this bone, where it meets the anterior 

 occipital arch, is thickened and consequently well defined from the 

 other bones. The anterior border of this thickened strip is in immediate 

 relation with the minute foramen of exit of the first occipital nerve, and 

 consequently this thickened portion of the bone exactly corresponds in 

 form as well as in its site to a third anterior semi-occipital arch that 

 has merged into the occipitalia lateralia. Now that the proof has been 

 furnished that vertebrae, originally separate, have blended with the 

 skull, an explanation can be given for certain points for examination 

 that are to be found upon the inferior aspect of the basioccipital, which 

 have not been alluded to by me before, because their significance would 

 not have been understood. 



Between the two posterior limbs of the parasphenoid, immediately 

 behind the two lower exits of the vascular canals described above, 

 that pass through the basioccipital, one finds two small pieces of car- 

 tilage, quite superficially placed upon the surface of the bone. (Plate I, 

 Fig. 2, X.) On viewing the vertebral column of this fish from beneath, 

 one can satisfy himself that very similar pieces of cartilage are upon 

 each vertebral centrum ; indeed, in younger individuals these cartilages 

 penetrate deeply into the substance of the centra, while in the older 

 specimens only very thin cartilaginous pieces can be recognized rest- 

 ing superficially on the vertebrae. 



*8Staniuu8, Da8 jaeripherisGhe Nervenaystem der Fisohe, pag. 119. 



