. Cunningham's Text-book of anatomy. Anatomy. ELEMENTS OF THE CENTRAL KERYOITS SYSTEM. 501 neural plate crista neuralis skin in a way that seems at first sight utterly abnormal, until it is remembered that they afford examples of very primitive methods of nerve- formation. The essential part of the organ of hearing is an ecto- dermal sac (otic vesicle) that develops as a diverticulum on the side of the head, from a thickened patch of ectoderm, which in the lower vertebrates forms part of a more exten- sive area, known as the dorso- lateral placode. Some of the cells of this area seem to be- co
. Cunningham's Text-book of anatomy. Anatomy. ELEMENTS OF THE CENTRAL KERYOITS SYSTEM. 501 neural plate crista neuralis skin in a way that seems at first sight utterly abnormal, until it is remembered that they afford examples of very primitive methods of nerve- formation. The essential part of the organ of hearing is an ecto- dermal sac (otic vesicle) that develops as a diverticulum on the side of the head, from a thickened patch of ectoderm, which in the lower vertebrates forms part of a more exten- sive area, known as the dorso- lateral placode. Some of the cells of this area seem to be- come transformed into nerve- cells, which migrate into the space between the otic vesicle and the neural tube (Fig. 443) and form the acoustic ganglion. At the upper margins of the branchial clefts a series of o^torium ectodermal (and possibly also D entodermal) thickenings develop, which are known as the epi- branchial placodes. Com- parison with the process of development in fish embryos, which has been elucidated by Landacre {Journal of Compara- tive Neurology and Psychology, 1910-1912), suggests that the nerve-cells may arise from these placodes, from which the nerves of taste originate. Fig. 442.—Diagrams of Transverse Sections representing Three Stages (A, B, and C) in the development of a Sensory Ganglion from the Neural Crest ; and Two Diagrams (D and E) suggesting a Possible Homology of the Olfactory (D) and Visual (E) Epithelium with the Neural Crest. Ganglion geniculi Xervus facialis Epibranchial placode of facial nerve. 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 Cunningham, D. J. (Daniel John), 1850-1909; Robinson, Arthur, b. 1862, ed. New York, W. Wood
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectanatomy, bookyear1914
