754 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [8] 



bones of tlie first group. The two osseous layers can also be distin- 

 guished in them, but the inferior one is better developed and more plen- 

 tifully supplied with Haversian canals, so that it becomes quite spongy 

 in character. As already stated, they are separated from the underlying 

 cartilage by a thin layer of connective tissue, through which ramify a 

 numerous set of vessels, and in which are found pigment cells. 



Finally, the postfrontals and prefrontals present us true " primary" 

 ossifications of the primoidal cranium, which cannot be removed without 

 injury to it, and which only remind us of their original development as 

 dermal bones by their superficial location and by their sculptured sur- 

 faces, the former also by their having mucus canals. 



The conclusion which we arrive at after our examination of these two 

 bones in Amia, and which they afford, is so unique and so unlike the 

 usual conditions that characterize those specific differences between 

 dermal bones and the ordinary ossifications of the true skeleton, that it 

 is easily perceived how Bridge was induced to separate each of these 

 bones into two components, and to distinguish the true — corresponding 

 to the homologous bones of the Teleostei — prefrontal and postfrontal, as 

 well as the " dermoprefrontal and dermopostfrontal," covering the same. 

 An unprejudiced examination at once convinces us that the conclusions 

 arrived at by Bridge do not agree with the actual condition of things. 

 The plates of these bones, visible on the surface of the cranium, as well 

 as the outer layer of all the other dermal bones, undoubtedly consist of 

 a compact and very hard bony substance, while those parts which are 

 more deeply situated are more cancellous in texture ; still the transition 

 of one to the other is gradual, and the superior plate cannot be removed 

 without breaking the bone. 



Sere a rare case presents itself — up to the present time almost universally 

 doubted — in which bones that on their surface present all the characteristics 

 of dermal bones have acquired relations with the true sTceleton through 

 their more deeply situated parts or structure^and in consequence are in part 

 dermal and in part true bones. 



Another group of bones is to be seen — partly, also, without dissection — 

 from the cavity of the mouth. Lying in the median line and longitud- 

 inally placed upon and belonging to the parasphenoid is an osseous 

 strip that is entirely covered over with a growth of firmly implanted 

 and small conical teeth.^* Between these teeth the bone is covered by 

 a very thin layer of mucous membrane, which is only to be discovered 

 after careful search. 



Situated anterior to these median bony strips, there is on either side 

 a number (from 17 to 22) of strong conical teeth, which are supported 

 by the vomer. As the interstices among these teeth are filled in by a 

 thick mucous membrane, nothing can be seen of the bones from an 



" When Bridge speaks of roughness (asperities) of the parasphenoid, he does not 

 convey to us the correct idea or condition. This roughness is caused by these trttfl 

 teeth, and of this fact Franque was already cognizant. 



