812 EEPOET OF COMMISSIONER OF FISH AND FISHERIES. [66] 



atlas, supplied by tlie occiput in Amia, is upon a co-ossified vertebra. 

 (See Part I.) 



Nearly all objects in nature are best seen, studied, and appreciated in 

 direct lateral view, and to this aphorism the cranium of a fish offers no 

 exception. This will at once be recognized in the case of our present 

 subject the "Lady fish," a side view of the parts already examined, which 

 I have endeavored to execute with great care, being presented in Fig. 

 29, along with the greater portion of the palato-quadrate arch. The 

 shape of the curiously formed ethmoid (Uth.) is now easily seen, and its 

 relations with its neighboring bones better understood; while beneath 

 it the vomer shows but slightly, though enough of it can be observed in 

 order to expose the position of the series of minute teeth spoken of above. 

 The prefrontal is seen to be enormously developed. It meets its fellow , 

 in the median plane, each one being pierced near this region by a large 

 elliptical foramen. Between the anterior convex border of this bone 

 and the ethmoid we find a vertical lamina of bone articulating as shown 

 in Fig. 29 at Wa^. This element I take to be merely a plate of semi- 

 ossified cartilage, though an examination of Alhula in the flesh, on some 

 future occasion, may force me to a change of opinion. The true nasals 

 in the specimen must have been lost. The orbits are seen to be almost 

 completely separated from each other by a thoroughly ossified inter- 

 orbital septum, an extension forward of the co-ossified orMtosphenoids. 

 (Fig. 29 Os.) This septum is very naaterially added to by the broad, 

 vertical plate, afforded by the hasisphenoid {ib. B. S.) 



This bone also sends upwards and outwards an osseous limb to artic- 

 ulate with the alisphenoid (As.). The three sphenoidal bones men- 

 tioned surround the optic foramen, as shown in the figure. While the 

 prefrontal completely forms the anterior wall of the orbital cavity, the 

 frontal the vault, the parasphenoid the floor, we find, in addition to 

 the bones we have mentioned, that the posterior wall is largely formed 

 by the postfrontal and prootic. Altogether this cavity is a very thor- 

 oughly circumscribed one, so far as its osseous boundaries are con- 

 cerned. 



The posterior aspect of the postfrontal (sphenotic) assists the squa- 

 mosal in forming an extraordinarily deep pit in the region to the rear of 

 the upper and posterior angle of the orbit. This pit is bounded above 

 by the squamosal and frontal, anteriorly by the alisphenoid and post- 

 frontal, internally by the squamosal, which bone with the postfrontal 

 forms its floor; behind, it opens along a longitudinal concavity of the 

 squamosal. Immediately below this concavity we find the facet for ar- 

 ticulation with the hyomandibular, also formed by the squamosal in 

 part, its anterior moiety being constituted by the postfrontal— not an 

 uncommon condition among the Teleostei. 



The regions occupied by the \ asi- and exoccipital, the prootic and 

 other bones, are so well shown in the figure as not to need any special 

 description here. 



