560 FISHES. 



but closed as in the Cyprinidse, by the orbitosphenoids and 

 the ethmoid that unite with the pre-frontals, carryiag forward 

 the cranial cavity to the nasal bone, without leaving a mem- 

 branous septum between the orbits. But the supraoccipital 

 is greatly developed, and in many the post-temporal is united 

 by suture to the sides of the cranium. In numerous members 

 of the family the skull is enlarged posteriorly, by dermal 

 ossifications, to form a kind of helmet which spreads over the 

 nape ; the lateral angles of this production are formed by the 

 suprascapulse, augmented and fixed by suture, and the median 

 part is the extension of the supraoccipital, which is generally 

 very large, is connected anteriorly with the frontal, and pass- 

 ing backwards between the post-frontals, the parietals, the 

 mastoids, and the suprascapulse, goes past them all on to the 

 nape. The mastoids interpose between the post-frontals and 

 the parietals, so as to come in contact with the supraoccipital, 

 and the parietals but little developed are pressed to the back 

 part of the cranium, and in some instances wholly disappear. 



The suprascapula most frequently unites to the mastoid 

 by an immovable suture, which includes the parietal when 

 that bone is present, and extends even to the supraoccipital. 

 It gives out besides two processes, one of them resting on the 

 exoccipital and basioccipital, or wedging itself between them, 

 and the other going to the first vertebra ; sometimes a plate 

 from the exoccipital supports the same vertebra. This verte- 

 bra, though it presents a pretty continuous centrum beneath, 

 is in reality composed of three or four coalescent vertebrae, as 

 we ascertain by its diapophyses, by the circular elevations of 

 the neural canal, and by the holes for the exit of the pairs of 

 spinal nerves. There is great variety in the development of 

 the various processes of the bones we have mentioned, and 

 there is no less in the magnitude and connections of the first 

 three interneurals. 



In general in the species which have a strong dorsal 



