58 ALUS. [Vol. XVIII. 



vertical longitudinal sections, the ventral edge of the bone is seen 

 as an arc of a circle, as if the ossification of the cartilage had begun 

 on the outer, dorsal surfacfe of the chondrocranium, and from there 

 extended inward. In transverse sections the ventral edge of the 

 bone is everywhere nearly straight, as is also, in horizontal longi- 

 tudinal sections, its posterior edge. 



The dorsal surface of the ethmoid is somewhat rectangular in 

 general outline, its posterior edge being straight, its anterior edge 

 and end somewhat rounded and irregular, and its lateral edges 

 concave. The lateral portions of its posterior half or two thirds 

 are covered, on each side, by the anterior end of the corresponding 

 frontal, a median tapering surface of the ethmoid being left ex- 

 posed between the two frontals. The ethmoid, in this part, 

 slightly overhangs, on either side, the nasal pit, and the frontals 

 slightly overhang the ethmoid. Immediately under and in front- 

 of the front end of each frontal there is, in the ethmoid, a strong 

 process projecting laterally, or laterally and slightly forward. It 

 is relatively thin, its dorsal surface lies on a level with the dorsal 

 surface of the ethmoid, and it gives support, on its posterior edge, 

 to the front end of the frontal. On its outer end it supports the 

 nasal, lying immediately ventral to the mesial edge of that bone, 

 slightly in front of the middle of its length. It is not capped with 

 cartilage, is not an articular process, and may be called the dorso- 

 lateral process of the bone. From its anterior edge there arises 

 a ligament, which runs downward and forward and is inserted 

 on a process on the outer surface of the maxillary near the ventral 

 edge of the anterior end of that bone. Directly ventral to this 

 dorso-lateral process, at the ventral edge of the ethmoid, there 

 is a second lateral process. It is directed laterally, downward, 

 and forward, is much stronger than the dorsal process, and is 

 capped with cartilage, the cartilage of the cap being always, in 

 small fishes, and often in large ones, continuous, along the ventral 

 surface of the process, with the cartilage of the base of the 

 chondrocranium. This second process is thus a process of the 

 chondrocranium, strengthened by the ethmoid bone which grows 

 downward upon and around it. It gives articulation to the 

 palatine bone, near its anterior end, and so fulfils, in this respect, 

 the function of that process of cyprinoids that is described by 



