A treatise on zoology . own type of end-organ,its OAvn set of nerve-fibres, and its own special nerve-centres(Strong [428], Herrick [210], Johnston [249]). It is further con-jectured that the general cutaneous and splanchnic sensorysystems, with their more specialised derivatives, and the motorsystems, may each have originally been represented in everysegment of the body. The size of nerve components in a given region is proportional NERVE COMPONENTS to the development of the end-organs they supply. Somesystems may increase in importance; others may dwindle or dis-appear altogether. Thus, the
A treatise on zoology . own type of end-organ,its OAvn set of nerve-fibres, and its own special nerve-centres(Strong [428], Herrick [210], Johnston [249]). It is further con-jectured that the general cutaneous and splanchnic sensorysystems, with their more specialised derivatives, and the motorsystems, may each have originally been represented in everysegment of the body. The size of nerve components in a given region is proportional NERVE COMPONENTS to the development of the end-organs they supply. Somesystems may increase in importance; others may dwindle or dis-appear altogether. Thus, the splanchnic components, so small inthe spinal nerves, are much developed in the head-region; theacustico-lateral system, so extensive in the fish, survives only in theear of the land vertebrate. We may now briefly analyse the nerves of a fish into their chiefcomponents (Fig. 12). A typical spinal nerve is formed by thejunction of a dorsal ganglionated root, containing a large general to. t^fo oA^au.^ i.^^-^^^rd. ^ £U. Fig. 12. Diagiarii of the iierve-eoiiii>onents in the head-region of a (chiefly aftharyiigeal ; an, auditorius (8); txi, r. buccalis(7); fo, r. ophthalmicus snjierfieialis (7); r\, branchial slit ; gl, glossopharyngeus (.); ?!, (7); iv, r. intestinalis (io); Ir, r. lateralis (10); mil, x. mandibularis (5);rax, r. luaxillaris (.j); oe, motor oculi (3); or, outline of orbit; j), patheticus (4); j/f», r. pala-tinus (7); pr, profundus ; jn/, r. pretrematicus (10): J5S)>, r. pretrematicus (7); pt, r. post-trematicus (10) ; ril, r. dorsalis; rf, r. recurrens (7); , spinal ganglion ; y?c, r. supra-teniporalis (10); tg, r. suprateniporalis (9); to, r. optlialmicus superticialis (5) ; , ventral rootof spinal nerve. Between the vagus and tlie lirst spinal nerve are some spino-occipital ne
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Keywords: ., bookcentury1900, bookdecade1900, bookpublishe, booksubjectzoology
