. Anatomy, descriptive and applied. Anatomy. THE BRAIN OR ENCEPHALON 851 The simple brain tube expands very early in intrauterine life in a sac-like manner, with the formation of three dilatations or pouches—the primary brain vesicles—demarcated by two constrictions.' The vesicles are designated respec- tively the Fore-brain (Prosencephalon). Mid-brain (Mesencephalon). Hind-brain (Rhombencephalon or Metencephalon). NEUROPORE -\. l_2 Fio. 620.—Brain tube of embryo salamander, sagittal section, showing neural segmentation (neuromeres): ~lll. Fore-brain neuronieres. M. Mid
. Anatomy, descriptive and applied. Anatomy. THE BRAIN OR ENCEPHALON 851 The simple brain tube expands very early in intrauterine life in a sac-like manner, with the formation of three dilatations or pouches—the primary brain vesicles—demarcated by two constrictions.' The vesicles are designated respec- tively the Fore-brain (Prosencephalon). Mid-brain (Mesencephalon). Hind-brain (Rhombencephalon or Metencephalon). NEUROPORE -\. l_2 Fio. 620.—Brain tube of embryo salamander, sagittal section, showing neural segmentation (neuromeres): ~lll. Fore-brain neuronieres. M. Mid-brain neuromeres. H. Hind- brain neuromeres. (Adapted from Kupffer.) i-PROTOVERTEBRA I. Fig, 621.—Brain tube of chick (25j^ hours), showing partly closed brain tube with eleven folds or neuromeres. (After C. Hill.) This classification has been found acceptable from every com- parative standpoint in brain mor- phology, but attempts have been made to establish a further seg- mentation into definite anatomical divisions regarding which opinions and usages differ widely and have proved to be a hindrance, rather than an aid to the homologization of brain structures in the vertebrate series. The difficulties in formu- lating a satisfactory schema of the segmental divisions of the brain will be overcome, perhaps, only by distinguishing the neuromeres or neural segments conforming to. the general segmental plan of the vertebrate body. The existence of a neuromerism that is akin to the metamerism or serial segmentation of the body, or to the branchiomerism characterizing the arrangement of the branchial arches, is indicated in several ways, but thus far only the earliest embryonic. 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 Gray, Henry, 1825-1861; Spitzka, Edward Anthony, 1876-1922. Philadelphia,
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectanatomy, bookyear1913
