138 
MR. W. K. PARKER ON THE STRUCTURE AND 
of Professor Huxley’s nomenclature of these parts, if it be held in mind that the prefixes 
signify physiological relation and not morphological representation. 
I make these remarks now because, when once fairly started, it will be necessary to 
keep clear of all other Vertebrate types: a comparison of the Frog with itself, in its 
marvellously varying morphology as its structure is traced from the egg to the adult 
form, will give us sufficient employment for the time. 
My object in this paper being special , I shall describe what has been seen without 
reference either to the works of other anatomists, or to what I am familiar with in the 
structure of the skull in other types. 
But as the Frog has received large attention from the best writers, it may be truly 
supposed that I am greatly indebted to their writings, the most important of which are 
the following, namely : — 
I. Ant. Huges. “ Recherches sur 1’Osteologie et la Myologie des Batraciens a leurs 
differens ages.' 5 Paris, 1834. 
II. K. B. Reichert. “ Vergleichende Entwickelungsgeschichte des Kopfes der 
nackten Amphibien, nebst den Bildungsgesetzen des Wirbelthierkopfes im Allgemeinen 
und seinen hauptsachlichsten Variationen durch die einzelnen Wirbelthierklassen.” 
Konigsb. 1838. 
But in endeavouring to form a clear conception of the morphology of the skull in its 
simple condition, I am most of all indebted to Jon. Muller’s magnificent work on the 
lower types of Fish, entitled “ Vergleichende Anatomie der Myxinoiden, der Cyclostomen 
mit durchbohrtem Gaumen.” Berlin, 1835. 
This work, Professor Huxley’s Croonian Lecture (Proc. Roy. Soc. Nov. 1858), and 
his ‘ Elements of Comparative Anatomy,’ 1864, have been always open before me whilst 
engaged in this piece of research. 
My observations on the structure of the skull in the Common Frog have, in several 
stages, been corroborated by what I have seen in JRana loans vel pipiens, Pseudis para- 
doxa, and Bufo vulgaris ; these, however, will be described at some future time*. 
Before commencing a description of the stages of the Frog, it is necessary to speak of 
the terms which will be made use of, both histological and morphological. 
In my memoir on the Shoulder-girdle (Ray Soc. 1868, p. 4), the varieties of ossification 
are spoken of as “ parostoses,” “ ectostoses,” and “ endostoses ; ” to these another variety 
might have been added, namely, “ dermostoses.” 
But the endosteal mode of ossification is further divisible into three kinds, namely, 
superficial, subcentral, and central endostosis. 
These distinctions hold good in many cases, whilst in others they completely break 
down, and therefore they have only a limited and varietal value. For instance, the 
three divisions of the parasphenoid in the Bird, as I showed in my last paper, are true 
* I have been greatly helped as to materials by Dr. Murie, Professor "W. H. Flower, F.R.S., Dr. Gunther, 
F.R.S., and Dr. HicRael Foster ; but the best help of all has been frequent discussion of the matter, in its 
gradual unveiling, with Professor Huxley. 
