174 NERVE COMPONENTS OF BONY FISHES. 



Cottus, Cyclopterus, Gadus, Tincta, Salmo, Alosa, Clupea 

 ('49, p. 77). In Belone and Esox he gives its innervation 

 from the r. palatinus VII (his r, palatinus V, p. 56), 



It is clear that in these two cases either the pseudo- 

 branch is not homologous or that a very remarkable 

 secondary shifting of nerve connections has taken place. 

 Now, the teleostean pseudobranch may be conceived of as 

 the vestige of any one of three demibranches of a lower 

 form : 



(i) The hyoid demibranch in the first gill cleft. 



(2) The hyoid demibranch in the spiracular cleft, 

 /. ^., the cephalic demibranch of the hyoid arch, or 



(3) The mandibular demibranch of the spiracular cleft. 



The first would be supplied by the pre-trematic IX 

 nerve, the second by the post-trematic VII (/. ^., the hyo- 

 niandibular or hyoideus, the third by a pre-trematic VII 

 nerve. 



The older writers assumed that the pseudobranch in 

 teleosts is a hyoidean gill, presumably the more caudal 

 demibranch, though the latter point is not usually made 

 plain. See particularly the paper by Maurer ('84). But 

 in a second paper Maurer ('88) traced the embryology of 

 the arterial arches in the salmon and found that it is not 

 the first (mandibular), but the the second (hyoid) arterial 

 arch that atrophies. The pseudobranch therefore de- 

 velops, we infer, in connection with the mandibular arch 

 and is a mandibular demibranch of the spiracular cleft. 

 This is further supported by the fact that in the forms in 

 which the pseudobranch is said by Stannius to be inner- 

 vated trom the VII nerve (Belone, Esox) its fibres come 

 from the r. palatinus, which is supposed to be pre-spirac- 

 ular, rather than from the r. hyomandibularis, supposed 

 to be post-spiracular. 



