MORPHOLOGY OF TELEOSTEAN HEAD SKELETON. 529 



with the ventral surface in reptiles, the pituitary fenestra has 

 a relatively different position in the two types, the resem- 

 blance becomes more striking. It is, therefore, possible to 

 regard this bone either as a pro-otic which has taken on the 

 functions of a reptilian basisphenoid; or a basisphenoid which, 

 like the exoccipital, has taken on relationships to the auditory 

 organ and a cranial nerve (cp. exoccipital). 



In the ethmoid region the general shape of the whole is of 

 considerable importance. Looked at from beneath (fig. 21), 

 after the removal of the nasals {na.'), it has the appearance 

 of a rectangle, somewhat expanded anteriorly and posteriorly, 

 with its long axis parallel to that of the skull, and, except 

 for a slight median groove continuous with that formed by 

 the fusion of the trabeculas behind, it is quite flat. The 

 expanded portions correspond to the pre-ethuioid and pareth- 

 moid cornua respectively. The former still serves as the point 

 of attachment for the palatine (fig. 51, pa.' ; fig. 31, e.pr., pa.). 

 From the middle of its dorsal surface arises the mesethmoid 

 in the form of a high longitudinal ridge of cartilage (figs. 32, 

 42, 51, em. c). Laterally and in front of this the ethmoid 

 retains its original plate-like character (cp. figs. 31, 32, 42, 



51, e.)- 



In describing the same region in Alepocephalus, Gegenbaur 

 calls attention to the fact that there it is normally broad, but 

 its anterior portion is drawn out into a terminally expanded 

 rostrum (78, p. 4), against which the projecting anterior 

 portion of the palatine bone abuts (p. 11), the whole differing 

 from that of the pike only in length (p. 4). Except for the 

 proportionately greater height of the mesethmoid ridge and 

 its more complete ossification, exactly the same might be said 

 of the ethmoid region of the stickleback (cp. Huxley, 71, 

 p. 132). 



The significance of this becomes more obvious when the 

 corresponding region is examined in the salmon. Luring 

 the developmental stages it shows a general resemblance to 

 that above described, but does not possess a terminal expan- 

 sion for the attachment of the palatine (Parker, 73, pi. v. 



