12 OSTEOLOGY OF SCOMBROID FISHES 



The epiotic is round in outline and elevated at its middle where the 

 posttemporal broadly and firmly articulates with it. It sends back a 

 thin horizontal shelf. 



The pterotic bears a wide ridge running obliquely upward from its 

 posterior end to the posterior end of the frontal. It bears a sensory 

 channel which is inclosed as a tube along its lower half, and is a deep 

 open canal along its upper. At its upper end this is in communication 

 upward with the frontal system of sensory tunnels, and downward 

 along the sphenotic with the suborbital system. At its lower end it com- 

 municates backward through the supratemporal with the lateral line 

 along the side of the body, and downward with the preopercular system. 



The prefrontals are not in contact with each other, though they are 

 separated only by a small area of cartilage apparently an unossified 

 part of the ethmoid cartilage. Each is pierced by the olfactory fora- 

 men. Near the upper end of each are two blunt spines, and the lower 

 end is a facet for the articulation of the palatine. The spines are ap- 

 parent externally through the skin in the undissected specimen. 



The ethmoid lies between the prefrontals and the anterior end of 

 the f rentals, separating the latter for a considerable distance. It may be 

 seen from below forming part of the orbital roof. In its anterior part, 

 on the superior surface of the cranium, an area of cartilage extends for- 

 ward and is continued along the posterior half of the vomer. This in 

 the dried skeleton shrinks and leaves an open channel. 



The vomer is toothless and ends below at its anterior end in a double 

 point. 



The nasals are slender, crooked bones continuing the sensory tube 

 from the frontals and carrying it forward. 



The suborbitals are represented by a preorbital plate and by some 

 thin, delicate bones behind the eye, but the chain is incomplete below 

 the eye. A long slender one extends up the side of the sphenotic, car- 

 rying the sensory tube up to the frontal, where it communicates with the 

 pterotic sensory tube and with the frontal tube. 



The supratemporal is an inverted T-shaped, tube-bone, its horizon- 

 tal branch continuing the lateral line to the pterotic sensory tube, its 

 vertical branch running upward to the top of the head at the side of 

 the supraoccipital just under the skin. Thence it runs backward along 

 the side of the supraoccipital spine nearly to the interneurals, resem- 

 bling the auxiliary branch of the lateral line common to many flounders. 



The hyomandibular is a long, rather simple bone, with a process be- 

 hind for the articulation of the opercle, and without a process to the 



