^16 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [70] 



frontals above and the alisphenoid and postfrontals below. In this 

 region, too, in the median line, we find that the alisphenoids and orbito- 

 sphenoids contribute to form a bony stanchion, that is directed forwards 

 ^nd upwards for the support of the frontal plates which rest upon its 

 apex. The alisphenoids are produced clear backwards to form a dome- 

 like surface, convex outwards, that is the anterior roof of the cranial 

 vault. In this the alisphenoids are assisted by the postfrontals on 

 either side, and both of these bones can be seen through the apertures 

 of this cavity behind (Fig. 33, As. and Ptf.). The sides of the roof ot 

 the cranium are formed by an incurved surface on the part of each 

 squamosal, while a somewhat similar surface, afforded by either exoc- 

 cipital, completes the parietes of the brain case in the rear. 



The form of the exoccipitals, the method in which they articulate 

 with the surrounding bones, and how they contribute to the formation 

 of the foramen magnum, is all well shown in Fig. 33, where these 

 bones are marked U. 0. A vagus foramen pierces each one on either 

 side of the foramen magnum, while, owing to the fact that the exit for 

 the optic nerves being so large, the parasphenoid can easily be dis- 

 <;erned through the latter opening (Fig. 33). The basioccipital forms 

 the lower arc of the periphery of the foramen magnum, as shown 

 in the figure. Its large articular facet is completely covered, through 

 the very interesting fact that it is so far anchylosed with the first ver- 

 tebra of the column that it is impossible to remove the latter in the speci- 

 men without doing it injury (see Plate XIX, Figs. 33 and 34, c. v.). 

 This is particularly interesting when we recall what has been said above, 

 in regard to the co-ossified vertebra of Amia^ found in this locality, as 

 well as the suspicious condition of affairs in these parts in Albula vulpes. 

 The suture between this vertebra in Megalops and the exoccipital is 

 distinctly retained, and may be traced completely around the bone. 

 Upon the upper side of this co-ossified or rather co-anchylosed vertebra 

 are seen two circular pits, of some little depth and size. Dr. Gill states 

 that these are intended to lodge the extremities of the neural arch. 

 They are placed side by side transversely and about a millimeter apart. 

 Two similar pits and similarly situated occur on the under side of the 

 vertebra. I am unable to pronounce upon these without first examin- 

 ing a recent specimen of this fish. 



Far as Megalops is removed from Amia calva, I still find in this old im- 

 perfect cranium from Professor Gill's cabinet plenty of food for thought — 

 with its suspicious-looking basioccipital vertebra, with its appropria- 

 tion of at least one trunk vertebra, with its sculptured frontals and other 

 bones raised above the cranium proper, with its more or less circular ali- 

 and orbito-sphenoids, and with the knowledge that a gular plate is found 

 between the rami of its mandible. 



We now return to our more typical Teleosteau, Micropterus salmoides, 

 and discuss other bones of its skull that I have as yet not touched upon 

 in this memoir. 



