24 



BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 



Ill older specimens this right supraorbital begins now to disappear, 

 the disappearance progressing from behind forward as the ensheathing 

 ocular-frontal takes its place and function. The remnant of this carti- 

 lage {ham. eth.), as it appears at a later stage, when it has been forced 

 into the horizontal position (vertical as the fish lies on its side), is shown 

 There is no longer a region of close appression without 



iu Figure D 



trh. .'fn''orb. dr. 



ecV">. .». 



Fig. C. 



Same model as that shown in Fig. C, viewed obliquely from right side and 

 behind. A probe is thrust through the right olfactory foramen. X 45. 

 . For meaning of lettering, see Abbreviations under Explanation of Plates. 



fusion between it and the median arch, but the hook arises directly from 

 the arch. 



In Figure Ca bristle is shown passing through the left olfactory for- 

 amen, to indicate the axis of the opening, ^'hich now is not parallel to 

 the longitudinal axis of the fish, — as the right olfactory foramen still 

 is, — but makes with it an angle of about 45 degrees, being directed 

 caudad, mediad, and dorsad. In Figure C a white probe marks the 

 position and direction of the right opening. 



