---------+------------------+-------------------------------- Segments.| Visceral clefts.| Dorsal nerve-roots and muscles. | | ---------+------------------+--------------+----------------- 1 | | V. N. op- | | | thalmicus | | | profundus | 2 | | V. | Masticating | 1st Mandibular | | muscles. 3 | | VII._1 |{Facial muscles | | |{(VIII. is dorsal | 2nd {Hyoid_1 | VII._2 |{branch of VII.) 4 | {Hyoid_2 | | 5 |3rd 1st Branchial | IX. | 6 |4th 2nd " | X._1 | 7 |{5th 3rd " | X._2 |Branchial and 8 |{6th 4th " | X._3} |visceral muscles. 9 |{7th 5th " | X._4 | ---------+------------------+--------------+----------------- As is seen in the table, van Wijhe attempts to arrange the cranial segmental nerves into dorsal and ventral roots, in accordance with the arrangement in the spinal region. In order to do this he calls the Vth, VIIth, IXth, and Xth nerves dorsal roots, although they are not purely sensory nerves, but contain motor fibres as well. It is not accidental that he should have picked out for his dorsal roots the very nerves which form Charles Bell's lateral series of roots, inasmuch as this system of lateral roots, apart from dorsal and ventral roots, really is, as Charles Bell thought, an important separate system, dependent upon a separate segmentation in the embryo of the musculature supplied by these roots. This segmentation may receive the name of _visceral_ or _splanchnic_ in contradistinction to _somatic_, since all the muscles without exception belong to the visceral group of striated muscles. {157}These observations of van Wijhe lead directly to the following conclusion. In the cranial region there is evidence of a double set of segments, which may be called somatic and splanchnic. The somatic segments, consisting of the outer skin and the body musculature, are _doubly_ innervated as are those of the spinal cord by a series of ventral motor roots, the oculomotor or IIIrd nerve, the trochlear or IVth nerve, the abducens or VIth nerve, and the hypoglossal or XIIth nerve, and by a series of dorsal sensory roots, the sensory part of the trigeminal or Vth nerve. But the splanchnic segments are innervated by _single_ roots, the vagus or Xth nerve, glossopharyngeal or IXth nerve, facial or VIIth nerve, and trigeminal or Vth nerve, which are mixed, containing both sensory and motor fibres, thus differing markedly from the arrangement of the spinal nerves.