368 COMPARATIVE ZOOLOGY OF CHORDATES 



The proprioceptive organs are innervated by nerves which 

 (in the head) run in to the brain through most of the cranial 

 nerves, including the oculomotor, trochlear, and abducens. 

 The ear, as an organ of balance, can also be considered as 

 belonging to the proprioceptive organs. 



The visceral afferent fibres collect impulses from the mucous 

 surface of the pharynx, mouth, and other viscera, and from 

 the taste sense-organs. In fish, the taste sense-organs are not 

 confined to the mouth, but may be found all over the surface 

 of the body. The afferent visceral fibres run in the branches 

 of the facial, glossopharyngeal, and vagus from the pharynx 

 and from the anterior and posterior faces of the gill-slits. In 

 the brain they converge in the medulla oblongata in the 

 visceral lobe or " taste-brain," beneath the centres for the 

 somatic afferent system. The visceral afferent system is also 

 called the communis system. The fibres innervating the 

 sense-organs of taste are sometimes regarded as forming the 

 special visceral afferent system, and they arise in relation to 

 the epibranchial placodes (see p. 194). 



The visceral efferent system is complicated by the fact that 

 the anterior end of the alimentary canal enters into relations 

 with the outside world. Its opening, the mouth,. is bounded 

 by the jaws which are under voluntary control, and so enable 

 the animal to aim at its prey and bite it. In connexion with 

 this, it is found that the muscles which actuate the jaws are 

 striated and voluntary, although they are visceral in origin. 

 The muscles attached to the gill-arches and which perform 

 respiratory movements are likewise striated. But although 

 voluntary and striated, these jaw and gill-arch muscles are not 

 innervated by ventral roots, for they are not derived from 

 segmented myotomes. Instead, they are innervated direct 

 by fibres of the special efferent visceral system which run in 

 the branches of the trigeminal, facial, glossopharyngeal, and 

 vagus, that pass down behind the mouth, spiracle, and the 

 several gill-slits respectively. In higher vertebrates, a portion 

 of the fibres of the vagus become grouped together more 

 posteriorly, and form the spinal accessory or nth nerve. 



The general efferent visceral system innervates smooth 



