976 



THE NERVE SYSTEM 



The following is a brief summary of the twelve pairs of cranial nerves, indicating 

 their functional nature: 



No. 



Name. 



Functional nature. "t 



I. 



II. 



III. 



IV. 



VIII. 



IX. 

 X. 

 XI. 



XII. 



Olfactory (fila). 

 Optic. 



Oculomotor. 

 Trochlear. 



V. ! Trigeminal. 



VI. Abducent. 

 VII. Facial. 



Nervus intermedium. 



Acoustic: 



I. Cochlearis. 

 II. Vestibularis. 

 Glossopharyngeal. 



Vagus. 



Spinal accessory. 



I. Accessory to vagus. 



II. Spinal part. 

 Hypoglossal. 



ttife***^* 



Smell sense. C^lr.T JU ** r b 



Visual sense.Oft-C ^r^T-.*-" 



Motor to muscles of eyeball and orbit. 



Motor to Superior oblique muscle of eyeball. |M 



Mixed: Sensor to face, tongue, and teeth; .motor .to 



muscles of mastication . 5. ^*i^ v *~ * 

 Motor to External rectus muscle of eyeball. 

 Motor to muscles of scalp and face. 

 Mixed: Sensor (gustatory) to tongue; e'xcitdglamlurar to 



submaxillary and sublingual salivary glands. 



Hearing sense. 



Equilibratory. 



Mixed-- Sensor (and gustatory) to tongue^nd pharymc; 

 motor (?) to Stylopnaryngeus muscle. *j >*i< ****>' ^ 



Mixed: Sensorimotor to respiratory tract anfl part of ali- 

 mentary tract. 



Motor to muscles of palate, pharynx, etc. ; respiratory 



gans; inhibitory to heart. ** w ' 



Motor to Trapezius and Sternomastoid muscles. . 

 Motor to muscles of tongue. K |L C^v^UtWV ^f. 



THE FIRST OR OLFACTORY NERVE (N. OLFACTORIUS). 



The olfactory nerves, or fila are the special nerves of the sense of smell, and are 

 about twenty in number on each side. These filaments constitute the first or 

 olfactory nerves and are the axones of the olfactory cells, lying in the small olfac- 

 tory region in the upper part of the superior turbinated process of the ethmoid 

 and corresponding portion of the nasal septum and are macroscopically differenti- 

 ated from the respiratory region in being of a more brownish hue (Fig. 726). 

 The olfactory fila are amyelinic and exhibit a plexiform arrangement in the deeper 

 layers. After piercing the cribriform plate of the ethmoid they become attached 

 to the under surface of the olfactory bulb, an oval mass of a grayish color, which 

 rests on the cribriform plate of the ethmoid bone and forms the anterior expanded 

 extremity of a slender process of brain substance, named the olfactory tract. 

 The olfactory tract and bulb have already been described (p. 928). The olfactory 

 tubercle (trigonum olfactorium) is a small triangular mass of gray substance between 

 the diverging roots of the optic tract (p. 929). 



Each nerve is surrounded by tubular prolongations from the dura and pia, 

 the former being lost on the periosteum lining the nose, the latter in the neuri- 

 lemma of the nerve. The nerves, as they enter the nares, are divisible into two 

 groups an inner group, larger than those on the outer wall, spread out over the 

 upper third of the septum; and an outer set, which is distributed over the superior 

 turbinated process and the surface of the ethmoid in front of it. As the filaments 

 descend, they appear to unite in a plexiform network, and are believed by most 

 observers to terminate by becoming continuous with the deep extremities of the 

 olfactory cells. 



The olfactory nerves differ in structure from other nerves in being composed 

 exclusively of amyelinic fibres. They are deficient in the white substance of 

 Schwann, and consist of axones with a distinct nucleated sheath, in which there 

 are, however, fewer nuclei than in ordinary amyelinic fibres. 



The central olfactory pathways are described on page 959. 



