928 



THE NERVOUS SYSTEM 



nerves corresponds at all closely with typical spinal nerves. This one is the 

 trigeminus which possesses a sensory ganglionated root and near its attachment 

 is accompanied by a small motor nerve, the masticator, which serves in very 

 small part as a corresponding motor root of the trigeminus. But even in this case 

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

 still points of anatomical difference, which if not essential are very obvious, for 

 the so-called motor root joins not the whole but only with one branch of the sen- 

 sory portion. The two are only slightly separated from each other at their attach- 

 ment 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 (olfactory ganglion) are scattered in the mucous membrane 



Fig. 731. — -Surface Attachment of the Cranial Nerves. 

 (After Allen Thomson, modified.) 

 Insula 

 y' Olfactory tract 



Hypophysis 



Anterior perforated 

 substances — ^ 



Corpora mammillaria. 



Cerebral peduncle 



Ganglion semi- 

 lunare (.gasseri.i 



Oblique fasciculus 



N. Hypoglossus (XII) 



Decussation of pyramids' 



N. opticus (II) 

 Optic tract 



- — Tuber cinereum 



N. oculomotorius 



(III) 



Lateral geniculate 



bodj 



- N. trochlearis (IV) 



/' \ N. masticatorius 



~'~' N. trigeminus (V) 



N abducens (VI) 



Brachium pontis 



N. facialis (VH) 



N. glossopalatinus 



N. cochlearis and N. 

 vestibularis (VIII) 



\ N. glosso-pharyngeus (IX) 



N. vagus (X) 



^^v N. accessorius (XI) 

 (spinal accessory) 



^^ Cervical I 

 ^Cervical II 



of the nose, an organ of special sense, and its fibres are not collected together into a 

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

 of the ethmoid bone directly into the olfactory bulb. The optic nerve is also a 

 nerve of special sense. Its fibres form a very distin(;t bundle, similar in appear- 

 ance to an ordinary nerve, from which, ho weaver, it differs essentially, both with 

 regard to structure and development; for, unlike an ordinary nerve, its connective 

 tissue consists to a large (!xtent of neuroglia instead of ordinary connective tissue, 

 and its component nerve-fibres are of much smaller calibre than those of an ordi- 

 nary nerve. It represents the location of the original optic stalk, a diverticulum 

 from the neural tube and it associates the retina (optic cup), a bit of modified cor- 



