[53] THE OSTEOLOGY OF AMIA CALVA. 709 



The alisplienoid develops two processes and is pierced by two fora- 

 miua. Of the processes, the smaller one arches over the canal for the 

 orbital muscles J the other is tlie " descending process of the alisphe- 

 noid." The larger foramen passes the first division of the fifth nerve ; 

 while the outer and smaller one transmits the second and third divis- 

 ions. 



In eack orbitosj)heuoid we sea a deep cleft to allow for the exit of 

 the optic nerve from the brain-case. They are supported by tho coa- 

 lesced trabeculae below, articulate with the alisphenoids laterally, and 

 support the cover-bones above. 



The eye-muscle canal ; the shallow pituitary fossa; the trabecular 

 groove ; the anterior clinoid process or wall, with the ossifications in its 

 substance; the "prootic bridge;" the openings of the carotid arteries; 

 and other structures in this region have all been sufficiently dwelt upon 

 in Part I. 



The lamina perpendicularis being in cartilage, Amia in consequence 

 lacks the true ethmoid found in Polypterus. In referring to the septo- 

 maxillaries Mr. Bridge says that "The two ossifications above referred 

 to as forming the autero-lateral angles of the internasal area are peculiar 

 to Amia amongst Ganoids. They lie, one on each side of the prenasal 

 process, and appear to be ossifications in the cartilage of the floors of 

 the nasal capsules; inferiorly they rest upon the upper surfaces of the 

 vomers. There can, I think, be but little doubt that these ossicles 

 (sep. mx.) [Fig. 3 and others of this paper smx.] are homologous with 

 the paired endosteal ossifications, which are to be found at the distal 

 end of the great i)rena.sal rostrum in the Pike. In fact, if the prenasal 

 region in Amia were produced anteriorly into a rostrum comparable to 

 that of the Pike, these bones would exactlj" resemble in position and 

 relations their homologues in the latter fish." 



"These ossicles would also appear to be homologous with the septo- 

 maxillary bone described bj' Mr. Parker as existing in the flow of the 

 nasal ca])sules in the Frog; and also with similar bones in the Ophidia. 

 A section carried through these bones and adjacent cartilage in Amia 

 would resemble in all essentials the various sections given in Mr. Parker's 

 paper (Phil. Trans , 1871) on the development of the frog's skull (PI. X)" 



The next step in our dissection is to carefully remove the suborbital 

 chain of bones; the maxillary and admaxillary; and the ganoid plates 

 overlying the nasal and premaxillary regions, then we have exposed in 

 the prepared skull the elements of the 



PALATO-PTERYGOID ABCADE. 



This is made up of the palatine, entopterygoid, ectopterygoid, with 

 which are associated the metapterygoid, hyomandibular, symplectic, and 

 quadrate. While intimately related to it is the preoperculum, and less 

 so the operculum itself, which latter merely articulates with the 

 hyomandibular. The entire arrangement of these bones in Amia is 



