the palato-pterygo-quadrate bar. AyERS and Jackson adduce no 
evidence in support of this view other than the fact just named. 
As STOCKARD says, these authors “interpreted the cartilage of the 
tooth-plate (in Bdellostoma) to be in reality lower jaw cartilage, but 
this, so far as I am able to gather from their paper, is all they con- 
tribute towards proving the matter”. STOCKARD himself contributes 
the information that the piston cartilage of Bdellostoma develops in 
the position in which it is found in the adult (!), and, though by his 
own showing there are no indications during development that the 
cartilage has ever been a paired structure (an anterior forking cannot 
be regarded as evidence in this connection), or that it ever had any 
connection with the supposed quadrate element, or that at any stage 
it borders the sides of the mouth in the manner characteristic of 
mandibular cartilages, yet nevertheless seems to consider that this 
information amounts to a demonstration that the piston cartilage 
must once upon a time have been a mandible. Now I think it is 
evident that the sole significance of the single fact of value (inner- 
vation of the piston musculature by the mandibularis) insisted upon 
by these authors is that it proves and solely proves that muscles 
belonging to the same region of the gut wall are habitually innervated 
by the same set of nerve fibres in all vertebrates, whatever function 
these muscles may possess, just as in vertebrates the muscles of the 
anterior appendage are always innervated by the brachial plexus 
whether these belong to a fin or to a pentadactyle limb. It is obvious 
that the mere fact that the muscles of the piston cartilage are 
innervated by the same nerve fibres which innervate the muscles of 
the mandible!) no more proves that the piston cartilage was ever a 
mandible than it proves that the mandible was ever a rasping organ. 
Such being the nature of the evidence upon which modern 
upholders of Gnathostome ancestry of the Marsipobranchs base their 
theory, it follows that if there exist any facts tending to show that 
the Marsipobranch head could never have possessed jaws, considerable 
1) Strictly speaking, the “‘ mandibular” nerve supplying the muscles of 
the piston cartilage is not homologous with the Gnathostome mandibularis— 
P. FÜRBRINGER (12), Jonnston (22)—since many of the motor fibres which run 
in the latter are found in the maxillaris of Marsipobranchs. Though this is 
but a small point yet it is some evidence that the visceral muscles of this 
region of the Marsipobranch body have never been arranged on the Gnatho- 
stome plan and have therefore never been concerned in the working of a 
mandible. 
