RAMUS PRE-TREMATICUS FACIALIS. I 75 



But if this argument from the innervation were followed 

 up, it would lead to the conclusion that in those species 

 which have the pseudobranch supplied by the IX nerve it 

 must be derived from the second hyoid demibranch, while 

 in fact Stannius states that the salmon itself, whose pseudo- 

 branch Maurer decided is spiracular, has that organ inner- 

 vated from the IX instead of the VII nerve. If, then, 

 Stannius is correct regarding the innervation in this species, 

 it follows that either the nerves or the arterial arches have 

 suffered profound secondary modification. And we are 

 not yet in a position to decide between these alternatives — 

 certainly not until Stannius' account of the inner\^ation 

 has been confirmed microscopically. 



From the neurological data now in hand it would 

 appear that the pseudobranch of bony fishes is some- 

 times a vestige of a demibranch of the first gill cleft, 

 sometimes of the spiracular cleft. It must be admitted, 

 however, that this mode of procedure may also lead into 

 difficulties, as e. g., in Lepidosteus (Wright, '85), where 

 the spiracular pseudobranch seems to be innervated by the 

 IX nerve and the hyoidean gill by the VII. But this case 

 requires further investigation, as all admit. 



At all events, pending further study, the case of ]\Ienidia 

 can be interpreted on the basis of the nerve supply in only 

 one way. We naturally assume that the pseudobranch 

 represents a mandibular demibranch of a vanished spi- 

 racular cleft, and that the nerve supplying it and the roof 

 of the pharynx adjacent between the areas supplied by 

 the IX and palatine nerves is a true pre-trematic VII 

 nerve, such as is mentioned, e. g. by Stannius and by 

 Ruge ('97), in some sharks. This accords with the embry- 

 ological data in the case of the vascular arches of the 

 salmon and Lepidosteus. Muller ('97) has studied the 



