. Notes on the North American ganoids [microform] : Amia, Lepidosteus, Acipenser, and Polyodon, with three plates. Ganoidei; Fishes; Ganoide; Poissons. T^.'i^i^l'** 182 B. NATURAL Amphioxus appears to have only a medulla with a fourth ventri- cle. The part in ft'ont of the ventricle may be regarded as an un- differentiated representative of the brain of the higher Vertebrates (Langerhans (44, 297) says he finds a small olfactory lobe). In Myxine and Bdellostomd, Joh. Miiller (37), found no ventri- cle in front of the fourth, and no cerebellum. In a somewhat in- jured preparation of t
. Notes on the North American ganoids [microform] : Amia, Lepidosteus, Acipenser, and Polyodon, with three plates. Ganoidei; Fishes; Ganoide; Poissons. T^.'i^i^l'** 182 B. NATURAL Amphioxus appears to have only a medulla with a fourth ventri- cle. The part in ft'ont of the ventricle may be regarded as an un- differentiated representative of the brain of the higher Vertebrates (Langerhans (44, 297) says he finds a small olfactory lobe). In Myxine and Bdellostomd, Joh. Miiller (37), found no ventri- cle in front of the fourth, and no cerebellum. In a somewhat in- jured preparation of the brain of Myxine, I find what seems to be a thin and rudimentairy cerebellum ; and a median ventricle which extends forward to the base of the anterior pair of lobes, which Miiller and all other authors regard as the olfactory lobes. On each side at this point is a slit-like orifice leading into the cavity of the olfactory lobe. These can be no other than the foramina of Monro and lateral ventricles. The liemispheres are hardly dis- tinguishable from the olfactory lobes. The larger pair of lobes just behind, since they form the walls of a median ventricle must be regarded as the undifferentiated prothalami and thalamr. They differ from thoib of Ganoids in being connected above as well as below. But behind them are the conarium and the orifice of the optic ventricle just as in the brain of Lepidosteus. In Petromyzon Miiller found (87) the third ventricle only. In several well pre- served preparations of the brain of the large sea-lamprey (P. marinus, var. Americanus), I find at the anterior extremity of this median cavity, as in Myxine, a foramen of Monro leading intO' the olfactory or lateral ventricle. The thalami are closed above as in Myxine. The distinct lobes which project just behind the olfac- tory lobes are probably hemispheres. (See Appendix.) Miiller describes the optic nerves of the Myzonts as not crossing at all. Upon this ground, aa by the non-separation of the t
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Keywords: ., bookcentury1800, bookdecade1870, booksubjectfishes, bookyear1876
