THE SKULL OF THE SALMON. 93 



covered by two large membrane bones, the parasphenoid 

 (fig. 9, B, 9) behind, the vomer in front. A view of the 

 posterior end differs from that of the cartilaginous cranium 

 only in the fact that the end of the parasphenoid appears 

 lying ventral to the basi-occipital. 



The lateral view differs very markedly from that of the 

 cartilaginous cranium, there being a great development of 

 membrane bone in connection with the jaws and branchial 

 apparatus. Lying dorsally are seen the median ethmoid, frontal, 

 parietal, and supra-occipital as before. Lying external to 

 the middle of the median ethmoid is seen the small nasal 

 (fig. 11, 8), and below the hinder part is the lachrymal The 

 lachrymal (fig. 11, 9) forms the first of a series of seven small 

 bones which surround the orbit forming the orbital ring. 

 Of these the one lying immediately in the mid ventral line of 

 the orbit is the sub-orbital, while the one lying in the mid- 

 dorsal line and attached to the frontal is the supra-orbital 

 (fig. 11, 11). The orbit has a cartilaginous sclerotic in which 

 are two small ossifications (fig. 11, 13) laterally placed. 



BONES OF THE UPPER JAW. 



The palato-pterygo-quadrate bar is in a very different 

 condition from that of the dogfish, it is partially cartilaginous, 

 partially converted into cartilage bone, partially overlapped by 

 membrane bone. It is narrow in front but becomes much 

 broader and deeper when followed back. Its anterior end forms 

 the palatine which bears teeth, and in front is completely 

 ossified, while behind the cartilage is only sheathed by bone. 



Just behind the palatine the outer part of the cartilage is 

 ossified, forming two small bones, the pterygoid and meso- 

 pterygoid, while behind them is a larger, somewhat square 

 bone, the meta-pterygoid (fig. 11, 15). 



Below the meta-pterygoid is a tract of unossified carti- 

 lage, and then comes the quadrate (fig. 11, 18). 



