Royal Microscopical Society. 255 



stages of this Fish I have used the collateral light of the study 

 of these parts in Salmon. 



What seems to be a continuation of the axis of the skull in 

 front is, really, the " trabecule cranii," or first facial arch ; and 

 there is such a copious growth of hyaline cartilage that all the 

 primordial parts are fused into an immense beaked box. In front, 

 above, scattered ganoid plates represent, in a general way, the 

 nasals and prae-maxillaries, and under the conical snout one, two, or 

 three fibrous bones do duty for the specialized " vomer" of the 

 bony Fishes. Farther back, on the under surface, a huge bony 

 splint — the " parasphenoid " — forms a strong and elastic balk to 

 the main part of the skull and the contiguous vertebrae. 



Laterally, thin fibrous plates are applied to the dense mass of 

 cartilage, and these represent the " pras-frontals," " orbito-sphe- 

 noids," and " ali-sphenoids "; I find these in very young specimens; 

 in the adult they only lie like splints on the cartilage. These 

 plates are sub- cutaneous, or rather sub-mucous. They are formed 

 under the skin of the mouth and palate, and answer to the outer 

 plates, minus the ganoid layer. They are parts of the skeleton of 

 the skin that have begun to yield to the organic attraction of the 

 endo-skeleton, and to be used up in its metamorphic changes. 



In a young sturgeon, one foot long, for which I am indebted 

 to Frank Buckland, Esq., who sent it me at the instance of Dr. 

 Murie, I found very much of what is seen in the adult, but not all ; 

 yet the metamorphosis of the original parts was almost complete ; I 

 ought to have specimens from the roe. In this specimen, the second 

 prae-oral arch " pterygopalatine," had formed a very curious con- 

 nection with the first post-oral (" mandibular "). These two arches 

 being arrested in growth, as compared with the second post-oral 

 (" hyoid "), are so attached to that arch and swung upon it, that they 

 are capable of being protruded far from their original (embryonic) 

 position. Each pterygo-palatine cartilage is a crescentic plate 

 attached to its fellow of the opposite side, anteriorly, by a dense fibrous 

 band. But the posterior part of this plate (Fig. 1, pa. pg. q.) 

 belongs to the pier of the mandibular arch — not all the " pier," but 

 its lower half. To understand this, let the reader imagine the first 

 condition of the mandibular arch, to be a sigmoid rod ; this rod be- 

 comes segmented off into two shorter pieces above, and one longer 

 piece below. The upper or " metapterygoid " segment flattens out 

 into a three-cornered piece, and coalesces with its fellow-piece at the 

 mid-line, above the mouth-tube, and thus the lozenge-shape piece is 

 formed, as seen from below, Fig. 2 (mt. pg.). The next piece is 

 squarish, and performs a very common morphological feat ; namely, 

 its fore-edge becomes completely united to the hinder edge of the 

 " pterygo-palatine " plate (Figs. 1 and 2, pa. pg. q.) ; we thus get 

 the " pala to- quadrate," or great " sub-ocular " bar, so familiar to 

 ichthyotomists. And now we find most familiar bones applied to 



