THE SKELETON OF THE VERTEBRATE HEAP. 173 



area of the palatal vault. The next area of the vault consLsts, 

 as iu the turtles, of the ethmoidal ueurapopliyses (the so- 

 called " palatals "), uiiited along the mesial line, and much 

 elongated backwards. The posterior margin of the combined 

 ethmoidal ueurapophyses of the turtle forms the central part 

 of the free margin of the palate ; but the completion in the 

 crocodile of the deflected outer margin and central ridge of 

 the pterygoids into a double tube, or pterygoidean prolonga- 

 tion backwards of the nasal fossa?, produces a corresponduig 

 elongation of the palatal vault, which accordingly presents, 

 behind its ethmoidal, an extensive and broad pterygoidean 

 area, wliich thus completes the vault behind, as in certain 

 Cetacea and Edentata. The great elongation backwards of 

 the combined m axillary palatal plates, the coiTesponding 

 elongation of the combined ethmoidal ueurapophyses, and the 

 gi'eat breadth of the pterygoidean area, have displaced the 

 palate-bones so far backwards and outwards, that, separated 

 from the ento-pterygoids and the ethmoidal ueurapophyses by 

 a wide chasm, but retaining their connections with the maxil- 

 laries and pterygoids, and coming into contact with the malar, 

 they are, in fact, extruded from the walls of the nasal fossa?, 

 and from the palatal vault, and, thus disguised, have been 

 hitherto known only as "transverse bones," " adgustal bones," 

 " pterygoides externes," " ecto-pterygoids." 



The Nasal Fassa//c of the Cydostamous Fishes. — The cyclo- 

 stomes differ from all other fishes in possessing a tubular 

 passage, which, opening externally above the oral disk, passes 

 backwards to the combined olfactory capsules, and behind 

 which it terminates in a cul-dc-sac in the lanqtrey, but in the 

 myxine and bdellostoma communicates with the alimentary 

 and respiratory tract. 



The form and an-angement of the cartilages, which enter 

 into the formation of the walls of this tubular passage, have 

 been figured and minutely described in the classical memoirs 



