[65] THE OSTEOLOGY OF AMIA CALVA. 811 



while externally it meets the epiotic. Careful examination shows that 

 this plate belongs to the squamosal. At the base of each vertical epi- 

 otic plate is to be seen a stumpy process, formed by a separate segment 

 of bone, which I take to be the oplsthoUc. It articulates with the epi- 

 otic, exoccipital, and squamosal. On the outer side of each vertical 

 epiotic plate there is another very deep concavity formed entirely by 

 the squamosal, except such inner part of its entrance which is entered 

 into by the vertical epiotic plate just mentioned. It is near the opening 

 of this deep pit (1.25 •'™) on the inner hand that we have the oppor- 

 tunity to study the manner in which the squamosal furnishes the little 

 circular plate that appears superficially in the larger concavity, as 

 described above. 



The foramen magnum is of a cordate outline, with its base below. It 

 is directed, that is the plane tangent to its margins, somewhat down- 

 wards as well as backwards. Its boundary below is formed by the 

 upper surface of the basioccipital condyle, while its lateral margins and 

 apex are furnished by a bone shaped like a little saddle, which strad- 

 dles the exoccipitals (Fig. 29, c. v). This bone, but loosely united along 

 its median line above, articulates with these last-mentioned segments 

 throughout its entire anterior margin, and in the specimen in ray hand 

 is slightly movable. At its lower and outer angles are seen a minute 

 pair, one on either side, of postzygapophyses. This bone fails to come 

 in contact with the basioccipital, and were it removed the foramen mag- 

 num would then be formed entirely by the basioccipital and exocci- 

 pitals, though these latter would be without articular zygapophysial 

 facets for the first vertebra of the trunk. Dr. Gill expresses the opinion, 

 in which I concur, that this double bonelet is the neural arch of the first 

 vertebra of the column. This being the case, it is important to compare 

 it with the co-ossified vertebrae found in this situation in Amia. I would 

 not care to do this, however, until in possession of a recent specimen of 

 Albula as well as its young. The outline of the basioccipital condyle is 

 pentagonal, and it is deeply and conically concave. A large elliptical 

 foramen pierces the supraoccipital on either side beneath, at the angle of 

 its horizontal and vertical portion. Two small foramina are also found 

 on either side in the exoccipitals just before we arrive at the suture, 

 where tbey join the aforesaid free neural arch just mentioned. 



This completes my description of the posterior view of the cranium 

 of Albula, as far as I mean to carry it. I am well aware that these bones 

 may be differently construed, but the moment we do so it becomes 

 necessary to have the various segments articulate among each other in 

 a manner differing from the general rule they adhere to in the vast 

 majority of cases among teleosts. To satisfy himself of this fact the 

 reader has but to call the bone I have described as a neural arch of the 

 first vertebra, the united exoccipitals, and the result will soon be evi- 

 dent. We must remember, in this connection, that the facet for the 



