138 ROY L. MOODIE 
I have been unable to find any account of an analysis of fish 
brains; and am thus uncertain as to the relative amounts of 
resistent substances, such as neurokeratin. 
The brain case in all recent selachians and teleosts is very 
much larger than the brain itself. In the skate, Raja binoculata, 
from Puget Sound, for example, the size of the brain cavity is 
out of all proportion to the size,of the brain, which occupies 
only a small part of the space. We may safely assume that the 
brain case of Paleozoic fishes was similar in this respect, since 
we find such a general similarity in other characters. We must 
thus account for the beautiful preservation of the brain and the 
complete disappearance of the skull of the Coal Measures fish 
in some other way than by assuming that’ a cast of the brain 
case was formed before the dissolution of the partly osseous, 
partly cartilaginous skull. It is hardly conceivable that the 
brain was preserved by a sudden filling of the brain cavity and 
“a subsequent infiltration of the space occupied by the brain, 
after the dissolution of that organ. 
III. REVIEW OF FOSSIL SENSORY STRUCTURES 
It is the intention of the following pages to review the work 
done on fossil brains, to give a detailed account of the anatomy 
of the brain and ear of a small ganoid (?) fish recently discovered 
in shales near Lawrence, Kansas, and to append a bibliography 
of papers dealing with fossil brains and other neural structures. 
The plan of this review will be to proceed upward in geological 
succession from the earliest formation in which are found traces 
of sensory organs sufficiently well preserved to afford any knowl- 
edge of their structure. This will also be proceeding upward 
from the most primitive known vertebrates to the higher mam- 
mals. The following outline will facilitate an understanding 
of this review. 
Ostracoderms—traces of brain cavity, lateral and pineal 
eyes; sensory (lateral line) grooves (Patten, ’12) 
Selachians—Lateral line, muscle, kidney, skin (Dean, 
IDE VonIa ther ene kee Mem. Amer. Mus. Natl. Hist., vol. 9, pt. v, 1909) 
Arthrodires—Sensory (lateral line) grooves on cephalic 
plates (see Dean. Mem. N. Y. Acad. Sci., vol. 2, Pt. 
III, ’01, pp. 116-119) 
