1220 



HIM AN ANATOMY. 



Certain of the cranial nerves are entirely motor ; some convey the impulses of special 

 sense ; while others transmit impulses of both common sensation and motion. A 

 general comparison of these relations, as now usually accepted, is afforded by the 

 following summary : 



THE CRANIAL NERVES. 



Number. Name. 



I. OLFACTORY : 



II. OPTIC : 



III. OCULOMOTOR 



IV. 

 V. 



VI. 

 VII. 



VIII. 

 IX. 



X. 



XI. 

 XII. 



TROCHLEAR : 

 TRIGEMINAL 



ABDUCENT : 

 FACIAL : 



AUDITORY, 



(a) Cochlear division : 



(b) Vestibular division 

 GLOSSO-PHARYNGEAL : 



PNEUMOGASTRIC OR VAGUS; 



SPINAL ACCESSORY : 

 HYPOGLOSSAL : 



Function. 



Special sense of smell. 

 Special sense of sight. 

 Motor to eye-muscles and levator pal- 



pebrae superioris. 

 Motor to superior oblique muscle. 

 Common sensation to structures of head. 

 Motor to muscles of mastication. 

 Motor to external rectus muscle. 

 Motor to muscles of head (scalp and 



face) and neck (platysma). 

 Probably secretory to submaxillary and 



sublingual glands. 

 Sensory ( taste ) to anterior two-thirds of 



tongue. 



Hearing. 



Equilibration. 



Special sense of taste. 



Common sensation to part of tongue 



and to pharynx and middle ear. 

 Motor to some muscles of pharynx. 

 Common sensation to part of tongue, 



pharynx, oesophagus, stomach and 



respiratory organs. 

 Motor (in conjunction with bulbar part 



of spinal accessory) to muscles of 



pharynx, cesophagus, stomach and 



intestine, and respiratory organs ; 



inhibitory impulses to heart. 

 Spinal Part : Motor to sterno-mastoid 



and trapezius muscles. 

 Motor to muscles of tongue. 



Practical Considerations. Lesions may affect a cranial nerve within the 

 brain or in its peripheral portion. A central lesion clinically is one above the nucleus 

 of the nerve, and may be cortical or may encroach upon its intracerebral connections. 

 It may merely irritate the nerve or may paralyze it. By a peripheral lesion is meant 

 one involving the nucleus or the fibres of the nerve below the nucleus. 



THE OLFACTORY NERVE. 



The olfactory nerve (n. olfactorius), the first in the series of cranial nerves, 

 presents some confusion in consequence of the name, as formerly employed, being 

 applied to the olfactory bulb and tract as well as to the olfactory filaments struc- 

 tures of widely diverse morphological values. As already pointed out (page 1151), 

 the olfactory bulb and tract (Fig. 993), with its roots, represent, as rudimentary 

 structures, the olfactory lobe possessed by animals in which the sense of smell is 

 highly developed. It is evident that these structures, formerly regarded as parts of 

 the first cranial nerve, are not morphological equivalents of simple paths of conduc- 

 tion. On the other hand such paths are represented by a series of minute filaments, 

 the true olfactory nerves, that connect the perceptive elements within the nasal 

 mucous membrane with the rudimentary olfactory lobe. 



The olfactory nerves proper, some twenty in number, are the axones of the 

 peripherally situated neurones, the olfactory cells (page 1414), which lie within the 

 limited olfactory area. The latter embraces in extent on the outer nasal wall chiefly 



