96 
ME. W. K. PAEKER ON THE STRUCTURE AND 
much new light upon this difficult subject in his Hunterian Lectures, delivered at the 
Royal College of Surgeons of England in 1863. 
During that time, and since then, this subject has been frequently and warmly dis- 
cussed between Professor Huxley and myself ; although all that I have written hitherto 
upon Ichthyotomy has been incidental and in elucidation of higher types, yet, with the 
exception of the Bird-class, the Fishes have received most of my attention. 
In the present paper the nomenclature will be based upon Cuvier’s, as modified and 
made elegant by Owen and as corrected by Huxley. I shall, however, have to differ 
on several points from the last of these three anatomists. 
The most invaluable part of Professor Huxley’s labours is that which has given us 
the true auditory elements in the bony skeleton ; three of these are almost universal — 
namely, the “ prootic,” the “ opisthotic,” and the “epiotic.” Cuvier only recognized 
the second of these as necessary to the “ pars petrosa,” his “ r ocher the prootic was 
mistaken by him for the “ great wing of the sphenoid,” and the epiotic as part of the 
occipital arch, his “ external occipital.” But Cuvier, and Owen after him, were right 
in putting another element, their “ mastoid,” amongst the auditory centres ; and Pro- 
fessor Huxley was wrong in supposing this piece to be the “ squamosal.” I pointed 
out this error to him before his Lectures were in print ; hut he w r as doubtful about what 
I had long felt certain of, and called it my opinion (see note to p. 188 in his Elem. Comp. 
Anat.). In his new work, however ( £ Anatomy of the Vertebrated Animals,’ 1871, p. 153), 
this bone is put into its proper category : thus we ha ye four “ periotic ” bony centres. I 
now have to speak of another periotic bone, the nature of which I have long pondered over, 
namely the “ postfrontal.” This bone, which was so called by Cuvier, but has nothing 
in common with his Reptilian postfrontal (a mere postorbital investing plate), begins as 
a delicate tract of osteoblasts immediately outside the ampulla of the anterior semicir- 
cular canal ; another ossifying tract begins over the ampulla and arch of the horizontal 
canal, this is the “ pterotic;” a third over the ampulla of the posterior canal, this is the 
“ opisthotic a fourth over the arch of that canal, the “ epiotic whilst the fore edge 
of the periotic capsule is ossified by the “ prootic.” I thus anticipate my descriptions 
for the sake of starting fair in my terminology ; I propose the term “ sphenotic ” for the 
antero-superior or postfrontal bony centre. 
As soon as possible all the terms must be put into harmony with the facts of mor- 
phology, and terms that are applied to two different parts in different Classes must be 
got rid of if they can conveniently be spared. Thus the term prefrontal, which is applied 
to a mere investing bone in one case and to the lateral mass of the ethmoid in another, 
ought to give way, in one case to preorbital, and in the other to a true morphological 
term, namely “ ecto-ethmoid.” 
I have long ceased to use such terms as “ os transversum,” “ ectopterygoid,” and 
“ entopterygoid,” as they do not mean the same thing in the Fish as in the “Sauropsida ” 
and the Mammalia. Cuvier’s “ transverse” of the Fish is really the pterygoid, as Professor 
Owen has well shown : Professor Huxley calls it “ ectopterygoid whilst his ento- 
