. Elements of the comparative anatomy of vertebrates. Anatomy, Comparative. 154 COMPARATIVE ANATOMY of cortical gray matter is only distinctly differentiated from Rep- tiles onwards. No regular series of gradations can, however, be traced in this respect in the various groups. Connecting the two lateral halves of the fore-brain are certain transverse bands of nerve-fibres or commissures. An anterior comviissure is present in the posterior region of the secondary fore- brain, a middle in the primary fore-brain, and a posterior in the anterior part of the mid-braiu. In addition to these, others
. Elements of the comparative anatomy of vertebrates. Anatomy, Comparative. 154 COMPARATIVE ANATOMY of cortical gray matter is only distinctly differentiated from Rep- tiles onwards. No regular series of gradations can, however, be traced in this respect in the various groups. Connecting the two lateral halves of the fore-brain are certain transverse bands of nerve-fibres or commissures. An anterior comviissure is present in the posterior region of the secondary fore- brain, a middle in the primary fore-brain, and a posterior in the anterior part of the mid-braiu. In addition to these, others may be developed between the hemispheres, but only attain im- portance in Mammals : they are known as the corpus callosum and the fornix. The outer surface of the hemispheres in all Vertebrates below the Mammalia is more or less smooth : in the latter Class, convolu- tions igyri) separated by fissures {sulci) may be present. The â J L â â â â. Fig. 125.âUiagbammatic Longitudinal Section thkough the Skull and Beain of an (Ideal) Vertebrate Embryo. (In part after Huxley.) Be, basis cranii ; Oh, notochord ; SD, roof of skull ; NH}, nasal cavity; YH, secondary fore-biain (prosencephalon), showing the corpus striatum (C'«) at the base, and the olfactory lobe (O//) anteriorly ; ZH, thalamencephalon (primary fore-brain), which has given rise dorsally to the pineal body (epiphysis, Z), and ventrally to the infundibulum (/), to which the pituitary body (hypo- physis, H) is attached : anterior to this is seen the optic nerve {Opt), arising from the optic thalamus {Tho^; HG, posterior commissure ; J/i7, mid-brain (mesencephalon) ; HH, cerebellum (metencephalon, secondary hind-brain); NH, primary hind-brain (myelencephalon) ; Cc, central canal of spinal cord. convolutions consist of folds of the gray cortical substance, which cause a greater or less increase of the superficial area. From the thalamenceplialon, the ventricle of which is walled-in anteriorly by the lamina terminalis
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectanatomycomparative
