[69] THE OSTEOLOGY OF AMIA CALVA. H15- 



articulating with the epiotic behind, and the frontal and sphenotic in 

 front, {^q.) Laterally it forms the hyomandibular facet, and enters with 

 the opiathotic and prootic into the formation of a deep conical indenta- 

 tion, immediately below the facet in question. It has a strongly marked 

 and raised ridge, extending from its outer and posterior angle obliquely 

 to the corresponding angle of the frontal (Fig. 34). 



The hasioccipital occuj)ying its usual position, is much compressed 

 from side to side, notwithstanding its centrum behind is very large, with 

 raised periphery. Most of the antero-lateral region of the cranium of 

 Megalops is made up of the prootic [Pr. 0.). This bone is pierced by its 

 usual foramina, and meets its fellow of the opposite side in the floor of 

 the cranium. Upon the lateral view of this part of the skull, the most 

 striking feature is a thin lamina of bone, with its plane nearly parallel with 

 the hasioccipital, and formed not altogether unlike a diminutive hand. 

 This appendage seems to be developed on the part of the opisthotic, but 

 of its function I can say nothing until I am i^ermitted to make a dis- 

 section of a fresh specimen of Megalops. A posterior vieio of the cra- 

 nium of this fish reveals to us its most extraordinary structure, and one 

 that would not be suspected hardly from a direct lateral aspect; indeed, 

 not at all, if the vacuity were filled in, where I believe the parietals 

 really belong. 



To arrive at a good, description of the condition of affairs, as I find 

 them here, it will be necessary for me to describe one or two of the 

 bones seen on posterior view, and first among these the supraoccipital.. 

 Yiewed from above, this bone presents somewhat of an extensive sur- 

 face, being greatly convex from side to side, while it is carried forward 

 in the median line as a sharp process (Fig. 34, 8. 0.), and behind we 

 see developed a stunted, lamelliform "supraoccipital crest," extending 

 directly backwards, with a small foramen on either side of it. Behind, 

 this bone is represented by a vertical plate wedged in between the epi- 

 otics, a vacuity existing at its apex below. The epiotics are well shown 

 in Fig. 33 {JEp. 0.), and the manner in which they articulate with the- 

 exoccipitals and squamosals {E. 0. and Sq.). Now upon the anterior 

 aspect the supraoccipital and the epiotic on either side, chiefly the 

 former bone, go to form a plowshare-shaped projection, that forms the 

 hinder and upper part of the vault of the cranium. Beyond it lies 

 a convex surface, in the specimen formed of dried membrane ; this con- 

 stitutes the next section of the cranial vault. Upon the outer side of 

 either epiotic we observe a large elliptical opening ; these lead into a 

 capacious cavity that exists between the frontals, squamosals, and 

 other bones of the roof above, and the true outer cranial vault, com- 

 posed of the alisphenoids, prefrontals, squamosals, and other bones 

 below. This cavity is irregularly wedge-shaped, its base being behind 

 and its thin edge situated anteriorly. This latter part lies between the 

 orbitosphenoids below and the frontals above. As we proceed back- 

 wards the interspace becomes greater, and it is here bounded by ther 



