THE NERVOUS SYSTEM. 309 



white fibres known as the internal capsule. As it nears the cortex 

 the fibres spread out. To this is given the name corona racliata. 

 Between the lenticular nucleus and the cortex of the island of 

 Eeil is seen a thin sheet of gray matter : the claustrum. 



The white matter between the claustrum and the cortex is 

 known as the external capsule. On horizontal section of the 

 brain the internal capsule is seen to be bent upon itself, the inter- 

 val between the optic thalamus and the caudate nucleus. This 

 bend is called the genu. One-third of the capsule lies in front of 

 this bend, and is called the anterior limb ; the portion behind the 

 genu is called the posterior limb. 



The anterior limb, contains (1) fibres that pass from the 

 optic thalamus to the lenticular and caudate nucleus, (2) fibres 

 that pass from the optic thalamus to the cortex of the frontal 

 lobe, and (3) fibres that pass from the cortex of the frontal 

 lobe to pass to the nucleus pontis. 



The posterior limb contains (1) a continuation upward 

 of a portion of the mesial fillet and the superior cerebellar 

 peduncles, (2) the pyramidal tracts or. motor fibres from the 

 Rolandic area, (3) the fibres of the optic radiation, (4) the 

 fibres of the auditory radiation, and (5) the temporo-pontine 

 tract. 



The opposite sides of the brain are connected by the com- 

 missural fibres. Convolutions on the same s*de are connected by 

 association fibres. Projection fibres are those which unite the 

 cerebral cortex with nuclei in lower levels. They pass princi- 

 pally through the corona radiata. 



The cerebral cortex consists of four layers : the stratum 

 zonale, the layer of small pyramidal cells, the layer of large 

 pyramidal cells, and the layer of polymorphic cells. 



CRANIAL NERVES. 



The cranial nerves consist of twelve pairs, as follows : 



1. Olfactory, 8. Auditory (portio mollis), 



2. Optic, 9. Glosso-pharyngeal, 



3. Motorcs oculorum, 10. Pneumogastric (vagus, or 



4. Pathetici, par vagura), 



5. Trifacial, 11. Spinal accessory, 

 C. Abducentes, 12. Hypoglossal. 



7. Facial (portio dura), 



1. OLFACTORY NERVE, special nerve of smell. A number of 

 nerves (20) arise from the olfactory bulb or lobe of the brain. 

 Superficial origin of the tract by roots: internal from frontal 

 lobe, middle or gray root from the olfactory tubercle between 



