756 EEPORT OF COMMISSIONER OF PISH AND FISHERIES. [10] 



Leaving entirely out of consideration the arguments that can be ad- 

 duced in favor of a progressive development of Amia in the direction of 

 the bony fishes, and that the division of a bone into several parts is an 

 hypothetical process, the positive proof has been given us by Walther " 

 that the vomer of the pike is a parial ossification. Yet the present posi- 

 tion of the vomers in Amia is not the primitive one, and in order to get 

 around all difficulties involved in this question we must assume that 

 in still more pristine forms both these bones occupied a position more 

 remote from the mesial line, o» either side of the anterior extremity of 

 the parasphenoid, as in many existing Amphibia. 



The conclusion arrived at from these inferences — taken in connection 

 with the fact that the vomerine and palatine teeth of fishes are situated 

 in one and the same line, lying in the same arch — gives some coloring 

 to the supposition that the vomers of fishes originally constituted the 

 anterior overlapping segments of the palatine arch, as has been proven 

 by Hertwig for the Amphibia. 



To the "cover-bones" of the skull in Amia yet belongs another piece, 

 that with other forms is not so intimately related to the primodal cra- 

 nium. It is the intermaxilla (Plate I, Fig. 1, and Plate II, Fig. 6, Sm.). 



This is to be seen extended upon the cartilaginous base of the rhiual 

 . chamber, proceeding backwards from its arched and compact alveolar 

 process; this thin osseous ijlate encroaches to no small extent upon the 

 antorbital region. 



In the posterior portion of the nasal depression this i^late is pierced 

 by a large foramen for the passage of the olfactory nerve (Plate I, Fig. 

 l,ol). 



The integrity of the cartilaginous cover of the primoidal cranium of 

 Amia is thoroughly preserved throughout, being devoid of fenestrse or 

 other breaches in its substance of any kind whatever. 



In outline it resembles a triangle placed longitudinally, with its apex 

 cropped off anteriorly; it is generally level, and marked only by pit-like 

 impressions at the posterior lateral angles, and by a number of project- 

 ing processes, which are more or less ossified. The two anterior ones 

 are the antorbital processes (Plate I, Fig. 1), with their ossifications 

 already described — the prefrontals. At about the middle of the skull- 

 cover the postorbital processes project out laterally at each side, to- 

 gether with their ossifications, also described as the postfrontals (Plate 

 I, Fig. 1). 



The prominent posterior lateral angle of the- primoidal skull is oc- 

 cupied by the intercalare [opisthotic] (Plate I, Fig. 1, Jc). 



As we proceed towards the median line from the angle formed by the 

 intercalare we find rising on either side another process, situated not 

 quite so far behind, that is formed by the exoccipital (Plate I, Fig. 1, Ux.). 

 Between these processes, formed by the intercalare and exoccipital, ex- 



" J. Walther, Die Entwicklung der DecJckurcken am Kopfslcelet des Rechtes. Jenaische 

 Zeitschrift f. Naturwiss., Bd. XVI, 1882. 



