[23] THE OSTEOLOGY OF AMIA CALVA. 769 



The oculomotorius and the trochlearis pass out through the large 

 posterior foramen of the orbital region, at its posterior margin, the first- 

 mentioned nerve above and the second beneath it. 



Between these two nerves lies the group of straight eye muscles, of 

 which the rectus externus is contained to some degree inside the cranium, 

 and gives rise to the development of an eye-muscle caual. 



Just anterior to the eye muscles, yet partly lying between them, we 

 find the optic nerve, which in Amia is but feebly developed, owing to 

 the small size of the eye. The ophthalmic artery, quite large in Amia, 

 passes also into the bulbus with the optic. Between the last-named 

 structures lies a strong fibrous cord, which arises at the posterior lower 

 angle of the orbital cavity, to be inserted near the place of entrance 

 of the optic on the bulbus. This cord corresponds in every respect to 

 the eye supports in the Selachii. The two oblique muscles are inserted 

 into the anterior angle of the orbit. 



The nasal region of the primoidal skull of Amia is bounded behind 

 by the antorbital processes, and has the shape of a triangular plate, 

 bearing a superior median crest. With the exception of two small ossi- 

 fications, the entire region is cartilaginous. On the inferior aspect of 

 this region, situated mesially and in front of the antorbital processes, 

 lie two oblong cartilaginous articulating facets for the anterior extrem- 

 ity of the palatine arch ; the distal end of these touches the ossified 

 part of this region, the septom,axillare (Plate I, Fig. 3, and Plate II, 

 Fig. 5, Smx.). This is an osseous center that extends from .the lower 

 margin of the foramen for the nasal nerve to the lateral margin of the 

 prenasal cartilage, and with which the maxillary is movably articulated 

 at the latter place. The greater part of this small bone is covered above 

 by the intermaxillary, and only becomes visible after this bone is removed. 

 This bone has been declared identical by Bridge with the ossification 

 at the base of the nasal capsule of the frog (the septomaxillare) ; and 

 although I consider the homology thus assumed as at least improbable, 

 still I did not introduce a new name. 



It would appear to me more correct if Bridge had compared the two 

 small ossifications known to us, which occur at the extremity of the 

 cartilaginous rostrum of the Pike, with the septomaxillary of Amia, 

 with which, indeed, they correspond in position as well as in their re- 

 lation to the neighboring parts of the skeleton. 



The cranial cavity is egg-shaped, with the apex directed forwards ; that 

 about the labyrinth region presents two niche-like depressions, for the 

 concealment of the labyrinth, that are sharply defined as we proceed 

 backwards towards the hinder extremity of the brain case. In Amia, as 

 among the Selachii and Ganoids, this depression extends from the fora- 

 men magnum to the nasal fossae. Not all of the ossifications of the pri- 

 moidal cranium that are to be seen on the outer aspect are to be ob- 

 served on the inner walls of the brain case or in the connecting spaces of 

 the labyrinth ; on the contrary, quit© a number of them do not reach 

 H. Mis. 67 49 



