82 MR. W. K. PARKER ON THE STRUCTURE AND 
The skull of the Tadpole, evidently a most generalised structure, covered the whole 
question with a cloud of doubt. 
Since then, whilst wavering, I have collected copious evidence of what seems to me 
to be a true second pre-oral rudiment in the antorbital region, and a first or terminal 
rudiment in the front of the face. 
I have already shown (“ Batrachia, ’ Part II., and “Urodeles,” Part I., and in my 
papers on the “ Selachian and Avian Skulls ”) the very constant occurrence of an 
ethmo-palatine in several large natural groups of Vertebrata. 
Here, in the larva of Pseudis, I have shown this part partly segmented off, and 
when not segmented off, it is yet very distinct, and not to be misunderstood; it assumes, 
in fact ,four positions, each of which is like what is seen in the members, generally, of 
some large group or groups. 
This large and most remarkable conjugational bar is parallel with the skull in the 
two first stages (A and B, Plates 2 and 11). 
So it is in the Siluroid Fishes {e.g., Clarias capensis), where the palatine bone 
formed by the ossification of an autogenous cartilage (in these and other Teieostei) 
remains distinct, but has no “ ethmo-palatine” or ascending process, as in the Salmon. 
In the third stage (C) it is bent outwards and forwards; this is the natural form 
and position of its independent homologue in a large number of the “ Urodeles.” 
It afterwards turns round; but in doing this there is a time in which it is directly 
transverse, or at a right angle to the skull, as in Menobranchus. 
In Proteus anguinus, where it is not drawn forwards by a chondrified nasal capsule, it 
turns backwards, and so it does also in Notidanus, in the Skates generally, and in 
many Birds. 
In the Salmon, as in the adult Toad, the ethmo-palatine has its three regions well 
developed—an ascending, an anterior, and a posterior part; all these are well seen in 
the stage of Pseudis just described. 
Such a rudiment of the ethmo-palatine as exists in the adult of many Urodeles, 
where it has coalesced with the back and lower part of the nasal capsule, is seen also 
in the “Sauropsida” {e.g., Chamceleo, Dromoeus, Casuarius, and Struthio); wdrilst in many 
Birds it is separately ossified, and forms, as the “os uncinatum,” a most characteristic 
endoskeletal bone in the fore-palate. 
The foremost pleural rudiment is less widely distributed as the “ pro-rhinal,” or 
“recurrent trabecular cornu.” I should not be surprised if it turned out to be the 
serial homologue of the mandibular suspensorium, of the epi-hyal, and of the epi- 
branchial elements/"* 
* 1 have already mentioned (p. 18) that Professor Huxley and Mr. Baleouk do not take the same views 
bf these parts as Professor Milnes Marshall and I do. 
