958 



THE NERVOUS SYSTEM 



The cranial nerves, like the spinal nerves, are developed from cells of the primitive 

 neural tube and, beginning with the fifth pair downwards, all the sensory nerves are 

 developed from the cells of the neural crest like the sensory components or dorsal 

 roots of the spinal nerves. Otherwise between the cranial nerves and the spinal 

 nerves there are many important differences. Each spinal nerve has a dorsal or 

 sensory root, which springs from the cells of a spinal ganglion; a ventral or motor 

 root, whose fibres are processes of the nerve-cells which are situated in the walls of 

 the central system, and at their attachment to the surface of the cord the two roots 

 are some distance apart. Only two cranial nerves correspond at all closely with 

 typical spinal nerves; they are the fifth and the seventh nerves, each of which possesses 



FIG. 698. SURFACE ATTACHMENT OP THE CRANIAL NERVES. 



modified). 



(After Allen Thomson, 



INSULA 



< 1 1. FACTORY TRACT 



HYPOPHYSIS 



ANTERIOR 



PERFORA TED - 



SUBSTANCE 



CORPORA MAMMIL- 

 LAE! A 



CEREBRAL _ 

 PEDUNCLE 



GANGLION SEMI- 

 LUNARE (gasseri) 



OBLIQUE 

 FASCICULUS 



X. OPTICUS (II) 

 , OPTIC TRACT 



c TUBER CINEREUM 



N. OCULOMO- 

 ,,,- TORI US (III) 



LATERAL 



| ____ GEX1CULATE 

 BOD Y 



N. TROCHLEARIS 

 (IV) 



"--^ X. TRIGEMIXUS 



I.V. /'.) 



N. HYPOGLOSKUS (XII) ' 



DECUSSATION OF PYRAMIDS 



~^ N. 



(V) 



N. ABDITEXH 

 (VI) 



BRACHIVM 



1'ONTIS 



N. FACIAL!.-; 



( VII) 

 PARS IXTERMEDIA 



- X. ACUSTICUS ( VIII) 



\ N. GLOSSO-PHARYS 

 GEL'S (7-Y) 



A". VAGUS(X) 



ft. ACCESSORIUS (XI) 

 (spinal accessory) 



CERVICAL I 



_.. CERVICAL II 



a sensory ganglionated and a motor non-ganglionated root. But even in these cases, 

 where the similarity between the cranial and spinal nerves is greatest, there are still 

 points of difference, which if not essential are very obvious, for in the case of the 

 fifth cranial nerve the motor root unites not with the whole but only with one branch 

 of the sensory portion. In both cases the motor and sensory roots are only slightly 

 separated from each other at their attachment to the surface of the brain. All the 

 other cranial nerves differ in a still more marked manner from typical spinal nerves. 

 The first nerve is an afferent nerve whose cells of origin are situated in the mucous 

 membrane of the nose, an organ of special sense, and its fibres are not collected to- 

 gether into a nerve-trunk, but pass, as a number of small bundles, through the lamina 



