Nos. IAND2.] ANATOMY OF SCOMBER SCOMBER. 



57 



age. The two processes, and the connecting ridge, represent, with 

 the basisphenoid, all there is, in Scomber, of the cartilaginous or 

 bony interorbital septum usually found in fishes. The dorsal proc- 

 ess is flat, broad and blunt. The ventral process is narrower 

 and thicker than the dorsal one, and is pointed posteriorly. 

 Laterally to the dorsal process, between it and the postero-dorso- 

 lateral corners of the cartilage, there is, on each side, a wide and 

 deep indentation, the preorbital incisure (ip). Through it the 

 ophthalmic nerves leave the orbit and reach the dorsal surface 

 of the chondrocranium. Running forward and slightly laterally 

 from the incisure, across the dorsal surface of the cartilage, there 

 is a small sharp groove, which, near the anterior edge of the 

 antorbital process, becomes a nearly closed canal, and then leaves 

 the cartilage in a more or less pronounced notch, which is the 

 ethmoid incisure (ic). The groove and canal lodge, as in Ainia, 

 the united ramus ophthalmicus superficialis trigemini and ramus 

 ophthalmicus superficiaUs facialis. That part of the antorbital 

 cartilage that, on each side of the head, lies lateral to the groove, 

 is called by Parker, in Sahno (No. 50, p. 108), the ectoethmoidal 

 wing, or antorbital expansion of the mesoethmoid. The part that 

 lies between the two canals is called by him the mesoethmoidal 

 region and is considered as part of the culmen cranii. 



The Ethmoid (ETH) of Scomber is one of the three primary 

 ossifications of the antorbital part of the chondrocranium. It is, 

 in the adult, a median bone, but gives some slight indications of 

 having been formed either by the fusion of two lateral components, 

 or by the fusion of two lateral components with a single, median 

 piece. It is to all appearance entirely of primary origin, no indi- 

 cation whatever being found in it of a fusion of dermal and cartil- 

 aginous components. It is not traversed, in any part, by any 

 portion of the lateral sensory canals, and there are not even, so 

 fas as could be determined, any surface lines of pit organs in any 

 relation whatever to it. Its dorsal and lateral surfaces are ex- 

 posed in the prepared skull, and their edges lie, in every part, on a 

 level with the outer surfaces of the adjoining cartilage of the 

 chondrocranium. Its ventral surface is not exposed, lying inside 

 the cartilage, and being everywhere separated from the base of 

 the chondrocranium by a relatively thick layer of cartilage. In 



