[51] THE OSTEOLOGY OF AMIA CALVA. 707 



sphenoid (os.); the post-frontal (Psf.) ; the alisphenoid (As.) ; the pro 

 otic (Pe.) ; the epiotio (jE/d?.) ; the opisthotic ( Jc.) ; the exoccipital (01.) 

 uiid the lateral view of the co-ossified " occipital arches" of Sageniehl 



Lastly, viewing the cranium directly from behind (PI. Ill, Fig. 13), we 

 may see the opisthotic (Jc.) 5 the exoccipital [01.) ; the epiotic (Ux.) 

 and the rear view of the vertebrae that have coossitied with the occiput 

 Should the vomers and parasplienoid be allowed to remain on, these 

 may also be seen upon lateral views. 



As the preceding ])aragraphs give the differences in nomenclature 

 as used by Sagemehl and Bridge, it will be unnecessary for me to re- 

 mark upon it further in this connection. 1 will simply say here that 

 from this point on, I propose to adopt the terms employed by the lat- 

 ter author in designating the various bones. 



The vomers are cleft behind to admit the paxasphenoid, while thej' 

 are united for their anterior thirds by suture. 



Near its middle, the parasphenoid throws off" on either side a lateral 

 wing, which in e^ich case passes upwards in a curve to bound the pro- 

 otic anteriorly, lying between the foramina of exit for the fifth and 

 seventh nerves, and finallj^ terminates against the postfrontal. 



Viewed from below, the united premaxillcG form a crescent-shaped bone, 

 that supports a complete single row of sharp, incurved tenth. These are 

 second in point of size of the various teeth found upon this part of the 

 skull ; the largest being on the palatines, and the smallest on the pos- 

 terior margins of the maxillaries, that is if we do not take into consid- 

 eration those minute teeth found on certain areas of the bones of the 

 mouth. The ascending portion of the premaxillw is carried back be- 

 tween the nasals and the sub-nasal cartilage as far as the frontals, 

 being covered in this situation by the nasals and ethmoid. Each as- 

 cending i)roces3 is pierced near its center by an oval foramen for the 

 passage of the olfactory nerve. 



We now come to examine the chondro-cranium proper and the ossifi- 

 cations that take place in it. Eemoving the bones we have just 

 described, the remaining part, pyramidal in form, has its broad end 

 posteriorly, while it terminates in front in the prenasal process. The 

 cartilaginous vault is uupierced by any foramina, and neither promi- 

 nent otic or nasal projections exist, as seen in many of the Teleostei. 

 Accommodating itself to the form of the cranium, the brain- box passes 

 between the orbits to have its apical anterior end terminate between the 

 prefrontals against the hinder margin of the lamina perpendicularis, 

 which in turn terminates anteriorly in the ijrenasal process, referred to 

 above. 



The SHpraocoipital is absent and the hasioccipital is much elongated, 

 owing to the fact that it has appropriated two of the leading vertebrae 

 of the column, the neural arches of which ride it above. 



Exoccipitals are well developed, and contribute both to the peripheries 

 of the foramen magnum and the opening for the vagus. 



