. The biology of the frog. Frogs. THE NERVOUS SYSTEM 309^. Cerr// vertebrates the cerebellum is an organ of considerable size, but in the frog it is almost rudimentary. The optic lobes, which form the dorsal part of the mid- brain, are large rounded bodies lying just in front of the cerebel- lum. Their cavities, the optic ventricles, communicate with each other and also with the channel between the third and fourth ven- tricles. Below the optic lobes are the crura cerebri, which extend from the medulla to the cerebral hemispheres and form the floor of the mid-brain. The thalamencephalon is in
. The biology of the frog. Frogs. THE NERVOUS SYSTEM 309^. Cerr// vertebrates the cerebellum is an organ of considerable size, but in the frog it is almost rudimentary. The optic lobes, which form the dorsal part of the mid- brain, are large rounded bodies lying just in front of the cerebel- lum. Their cavities, the optic ventricles, communicate with each other and also with the channel between the third and fourth ven- tricles. Below the optic lobes are the crura cerebri, which extend from the medulla to the cerebral hemispheres and form the floor of the mid-brain. The thalamencephalon is in the region between the optic lobes be- hind and the cerebral hemispheres in front. Its roof is thin and lined with a vascular membrane, the anterior choroid plexus; it bears two outgrowths in the mid-dorsal line, the paraphysis, a vascular outpocketing of the epithelium of the roof, and a short distance be- hind the latter, the epiphysis, a hollow, thin-walled canal which terminates blindly at its anterior end. A small parietal nerve runs along the dorsal surface of the epiphysis and extends forward over the paraphysis and then passes through the sagittal suture of the skull to end in the brow spot. The epiphysis, which originally was continuous with the brow spot, becomes constricted off from it in early -Med. oil Fig. 102.—Diagram of a horizontal section of a frog's brain, , central canal; , cerebral hemisphere; Di, dien- cephalon, or thalamen- cephalon ; , fora- men of Monro ; i, iter ; , lateral ventricle; , medulla oblon- gata ; , first, or olfactory nerve; , olfactory lobe ; , ol- factory ventricle ; ; optic lobe; , optic ventricle; , spinal cord ; v3, third ventricle ; v4, fourth ventricle. (Af- ter Ecker and Wieders- heim.). 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 p
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