The involuntary nervous system / by Walter Holbrook Gaskell.

  • W. H. Gaskell
Date:
1920
Catalogue details

Licence: In copyright

Credit: The involuntary nervous system / by Walter Holbrook Gaskell. Source: Wellcome Collection.

    20/200 page 4
    myotomes ; the dorso-ventral muscles are found in the cranial segments and form the ocular muscles. This segmentation I have therefore called in both vertebrates and invertebrates the somatic segmentation. The striated muscles in the vertebrate, which are derived from the invertebrate appendage muscles, are situated mainly in the cranial region, and form two groups in the adult vertebrate ; (i) the muscles of mastication, which correspond to the muscles of the masticatory appendages in the invertebrate, and (2) the muscles of respiration, which correspond to the muscles of the respiratory appendages. Therefore the segmentation due to the appendages in the invertebrate corresponds to V. Wijhe’s ventral segmentation, which I have called splanchnic or visceral. In using the terms somatic and splanchnic to denote these two segmentations instead of the terms mesomeric and branchiomeric, I was dealing throughout only with striated musculature, so that the term somatic denoted a well-defined group of striated body muscles in contradistinction to another well-defined group of striated visceral or splanchnic muscles. It is therefore absolutely erroneous to make use of the term somatic as defined by me, as though it were synonymous with striated, as has been done by Edinger and by Langley and Anderson. In Limulus and the Scorpions the region which bears the masticating appendages has been called the prosomatic region, and the region which bears the respiratory appendages the meso- somatic region. The same terms may be used with advantage in talking of the corresponding regions of the vertebrate. The more primitive arrangement of the segmental motor nerves in the cranial region to supply the muscles belonging to the somatic and splanchnic segments, corresponding to the somatic and appendage muscles of the invertebrate, is naturally shown also in the origin of the motor fibres from the motor-cell groups in the cranial region. Thus in the prosomatic region (Fig. i) the nucleus masticatorius of the trigeminal together with the series of nuclei, which are described on the so-called descend¬ ing root of the trigeminal and give origin to the fibres of this so-called root, represent the motor neurons of the splanchnic segmentation, and represent therefore the motor neurons of the muscles of the prosomatic appendages ; they are quite separate from the oculomotor and trochlearis nuclei, which represent the
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