Nos. IAND2.] ANATOMY OF SCOMBER SCOMBER. 77 



cartilage become indistinct, or disappear entirely. The dorso- 

 mesial edge of the bone is edged with cartilage and bounds, in its 

 middle portion, the large dorso-lateral fontanelle of the chondro- 

 cranium. Posteriorly this edge of the bone bounds the temporal 

 interspace of cartilage. 



On the anterior, or orbital face of the ossification there is al- 

 ways a large and deep pit (ofc, Figs. 5, 9), from the hind end 

 of which one or two canals lead upward to the dorsal surface of 

 the bone, near its lateral edge. The pit, and one or both of the 

 canals, transmit the ramus oticus facialis from the orbit to the 

 dorsal surface of the skull, but the pit is much larger than need 

 be simply for the passage of the nerve. On the lateral surface of 

 the ossification there is usually, but not always, an opening, often 

 large, which leads into the hind end of this pit, but no nerve or 

 vessel could be found traversing it. Its position, so similar to that 

 of the ventral opening of the spiracular canal in Aiiiia, and its 

 relation to a canal that transmits the otic nerve, both seem to indi- 

 cate that it, or it and the otic canal together, represent rudiments 

 of the spiracular canal of the fish. 



The internal, or cerebral surface of the ossification is relatively 

 small. It presents two recesses, or pit-like depressions, separated 

 by a narrow, nearly vertical ridge of bone which projects back- 

 ward and mesially into the cranial cavity and represents a part of 

 the anterior bounding wall of the labyrinth recess. Both depres- 

 sions are, in the recent state, filled with fatty tissue. The anterior 

 and larger one has, in the adult, ho apparent relations to any of 

 the organs contained in the cranial cavity. The posterior one 

 apparently lodged, in larvae, the anterior end of the anterior semi- 

 circular canal of the ear. In the adult it does not, however, lodge 

 that canal, the canal turning upward considerably posterior to the 

 bottom of the recess. At the bottom of one or both of the recesses 

 a small foramen was sometimes found from which a short canal 

 leads toward or even into the large pit that transmits the otic 

 nerve. Although this canal, when found, did not seem to have 

 been artificially produced, there was nothing whatever to indi- 

 cate its significance. 



The Alisphenoid (AS) is a nearly rectangular bone, forming 

 somewhat more than half of the hind wall of the orbit. It inclines 



