148 INTRODUCTION TO NEUROLOGY 



4. Special somatic efferent nerves, supplying two groups of highly special- 

 ized somatic muscles, namely, the external eye muscles and a part of the 

 tongue muscles. They arise from a ventro-medial series of motor nuclei and 

 are represented in the III, IV, VI, and XII pairs. 



5. General visceral afferent nerves, innervating visceral mucous surfaces 

 without highly differentiated sense organs. They distribute through the 

 sympathetic nervous system and are represented in the VII, IX, and X pairs 

 and perhaps in some others. 



6. Special visceral afferent nerves, for the innervation of specialized sense 

 organs serving the senses of taste and smell. The gustatory fibers are 

 represented in the VII, IX, and X pairs. The olfactory nerve (I pair) is 

 probably a more highly differentiated member of this group (see pp. 91 

 and 215). 



7. General visceral efferent nerves, for unstriped involuntary visceral 

 muscles, heart muscle, glands, etc., distributing through the sympathetic 

 nervous system. These fibers (preganglionic fibers of Langely, p. 229) are 

 present in the III, VII, IX, X, and XI pairs. 



8. Special visceral efferent nerves, supplying highly specialized striated 

 muscles of a different origin (both embryologically and phylogenetically) 

 from the striated trunk muscles. These muscles are connected with the 

 visceral or facial skeleton of the head and are derived from the gill muscles 

 of fishes. These nerves in the adult body resemble those of the somatic 

 motor system, save that they arise from a different series of motor nuclei in 

 the brain (the ventro-lateral motor column) . They have no connection with 

 the sympathetic nervous system and are represented in the V, VII, IX, X, 

 and XI pairs. 



In the preceding Table of Nerve Components (pages 146, 147) the sev- 

 eral cranial nerves are analyzed and compared with a typical spinal nerve. 



The various functional systems of the head tend to be con- 

 centrated in one or a few cranial nerves for ease of central corre- 

 lation, and even in case a given system is represented in several 

 nerves, the fibers of this system may converge within the brain 

 to connect with a compact center. This is well illustrated by the 

 gustatory and acoustico-lateral systems of the cranial nerves of 

 the fish, Menidia, as shown in Fig. 65. Here the gustatory sys- 

 tem (indicated by cross-hatching) is present in the VII, IX, and 

 X cranial nerves, and all of these fibers, together with other 

 visceral fibers, converge within the brain to enter the visceral sen- 

 sory area in the vagal lobe (lob.X.). Similarly, the lateral line 

 components of the VII and X nerves and the VIII (printed in 

 solid black) converge to enter the acoustico-lateral area in the 

 tuberculum acusticum (t.a.}. The general cutaneous fibers 

 enter by the V and X nerves, and all of these fibers enter the 

 spinal V tract (sp.V.). 



In the paragraphs which follow the chief central connections (terminal 

 nuclei of the sensory systems and nuclei of origin of the motor systems, see 



