. Devonian fishes of Iowa. Fishes, Fossil; Paleontology; Paleontology. 268 IOWA GEOLOGICAL SURVEY here viewed from the dorsal aspect (Fig. 40 B1). The brain, to be seen in its natural position within the interior of the head, Fig. 40 A, is oriented in a corresponding fashion, and the nodule containing it is fractured in such manner as to cleave off the cranial roof, which latter is seen from the cerebral aspect in A1. Both specimens, A and B, show a relatively large-sized fish brain, as completely formed as in any modern teleost, and seg- mented in the usual manner. In the median line posterio
. Devonian fishes of Iowa. Fishes, Fossil; Paleontology; Paleontology. 268 IOWA GEOLOGICAL SURVEY here viewed from the dorsal aspect (Fig. 40 B1). The brain, to be seen in its natural position within the interior of the head, Fig. 40 A, is oriented in a corresponding fashion, and the nodule containing it is fractured in such manner as to cleave off the cranial roof, which latter is seen from the cerebral aspect in A1. Both specimens, A and B, show a relatively large-sized fish brain, as completely formed as in any modern teleost, and seg- mented in the usual manner. In the median line posteriorly is to be observed the funnel- shaped expansion of the spinal cord known as the medulla, which merges forwardly into a quadripartite organ well repre- sented at the base of Fig. 40 B1, which can scarcely be inter- preted other than the cerebellum or hindbrain. This organ is moderately large, probably correlating with the activity of the animal, just as the large size of the optic lobes is correlated with a keen visual sense, and the auditory ampullae with a well de- veloped faculty of equilibration. The two anteriorly situated lobes of the cerebellum are larger than the posterior pair, and diverge laterally so as to embrace the bilobed midbrain or mesen- cephalon, whose dorsal wall is constricted into two lateral por- tions known as the optic lobes. That the eyes were of impor- tance for this creature is betokened by the large size of the optic lobes, and also by the relatively wide orbital openings. The section of the brain lying immediately in advance of the optic lobes is that formed by the cerebral hemispheres, still cov- ered in one of the specimens (Fig. 40 B1) by a choroid a. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Eastman, Charles Rochester, 1868-1918; Iowa Geological Survey. Des
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