The somatic sensory components supply the skin, and end in cells which, among the cyclostomes and fishes, form a considerable elevation in the rhombencephalon, known as the nucleus quinti (fig. 8). These components, in the lower forms, are found in the fifth, seventh and tenth nerves, but in mammals practically only the fifth contains them. They correspond to the dorsal roots of the spinal nerves.
The splanchnic sensory or viscero sensory components end in the brain in the medullary cells known as the fasciculus communis in fishes, and named the fasciculus solitaries in mammals, as well as in the nucleus vagi (fig. 8). They are found in the fifth, seventh, ninth, tenth and eleventh nerves, and supply visceral surfaces. In mammals the lingual and palatine branches of the fifth, the chorda tympani and great superficial petrosal of the seventh, and all the sensory fibres of the ninth and tenth except Arnold's nerve, represent these. In fishes and Amphibians the palate is supplied by the seventh nerve instead of the fifth.
The system of the lateral line or acustico-lateralis component is sometimes regarded merely as a subdivision of the somatic sensory. It is best developed in the fish, and may be divided into pre- and post-auditory and auditory. The pre-auditory part comprises the pit and canal end organs supplied by the seventh, and also probably the olfactory organ supplied by the first nerve. The auditory apparatus, supplied by the eighth nerve, is, accord ing to modern opinion, undoubtedly a part of this system, while the tenth nerve sends a large branch along the lateral line supply ing the special end organs of the post-auditory part.
The following table, slightly modified from the one drawn up by J. McMurrich, gives a fair idea of the present state of our knowledge of the nerve components in the Mammalia.
*A tract of the brain.
BIBLIOGRAPHY.--For further details and literature of the nervous system see Quain, Anatomy (latest edition) ; R. Wiedersheims, Comp. Anat. of Vertebrates (London, 1907) ; Bronn, Classen and Ordnungen des Thierreichs, McMurrich, Development of the Human Body (Lon don, 1923). For the theory of nerve components see Onera Merritt, Journ. Anat. and Phys., vol. xxxix. A general discussion on the comparative anatomy and morphology of limb plexuses will be found in Miss C. W. Saberton's paper (1906), "Nerve Plexuses of Troglodytes niger," Studies in Anatomy (Manchester, 1906). She refers to most of the literature on the subject, but the papers of H. Braus, Jena Zeitschr. (1898), on fish, of M. Davidoff, Morph. Jahrb. (1879), on the pelvic plexuses of fish, and of M. Fiirbringer, Gegenb. Festschr. (1897), on the spino-occipital nerves and brachial plexus of fish, are also important. See also S. W. Ransom, The Anatomy of the Nervous System (Philadelphia, 1927 ; bibl.) ; A. Pitres and L. Testut, Les nerfs en schemas (Paris, 1925) ; L. Bianchi, The Mechanism of the Brain and the Function of the Frontal Lobes (Edinburgh, 1922 ; bibl.) ; J. R. Whitaker, Anatomy of the Brain and Spinal Cord (Edinburgh, 1921) ; C. U. A. Kappers, Die Vergleichende Anatomic des Nervensystems der Wirbelthiere and des Menschen (Haarlem, 192o-21; bibl.). (F. G. P.)