647 
superior of Ceratodus, while the ganoidean and teleostean arrange- 
ments would each arise by the differentiation of an internus either 
from the rectus inferior or the obliquus inferior, the order of inner- 
vation of the inferior and internus muscles being reversed in the two 
cases (ALLIS, 1903, p. 236). This would certainly seem to be a more 
simple and probable derivation of these muscles than the one I have 
recently (1904a) suggested in connection with the incorporation of 
the selachian eyestalk in the chondrocranium; and in favor of the 
derivation here suggested it is to be noted that GREIL apparently shows, 
in several of his figures, the obliquus inferior arising by two separate 
heads, as if two muscles were there in process of differentiation. 
The preparation and examination of the serial sections used in con- 
nection with this work has all been done by my assistant Mr. Joan Henry. 
Palais des Carnolés, Menton, May 26th, 1914. 
Literature. 
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Fishes. Proc. Washington Acad. of Sciences, Vol. 7. Washington 1905. 
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Amia calva, Journ. of Morphology, Vol. 12. Boston 1897. 
Autts, E. P. jr., The Skull, and the Cranial and first Spinal Muscles and 
Nerves in Scomber scomber, Journ. of Morphology, Vol. 18. Lancs 1903. 
Aruıs, E. P. jr., a) The Pseudobranchial and Carotid Arteries in the Gnatho- 
stome Fishes. Zoolog. Jahrb. Abt. f. Anat. und Ontog. der Tiere, 
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