THE NERVOUS SYSTEM 



stance, the gray forming the external layer and the white the internal. 

 The tree-like appearance presented when the cerebellum is cut in half 

 has been termed the arbor vitce. 



The cerebellum is divided into two hemispheres, and a central portion 

 named the vermiform process. At its base the white fibres forming its 

 fibrous substance are gathered together into three great strands, groups, 

 or peduncles, on each side; the lowest or most posterior connects it with 

 the lateral columns of the spinal cord. The middle group forms a great 

 part of the pons, ^ ^ 



and crosses to the * ° ' t 



opposite hemisphere, 

 while the third group 

 runs forward to the 

 cerebrum. 



We have seen 

 that forty - two or 

 forty -three pairs of 

 nerves arise from the 

 spinal cord. Twelve 

 more pairs arise from 

 the brain and parts 

 within the cranium, 

 and are termed ce^e- 

 hral nerves. From 

 the importance of 

 the parts the latter 

 supply they have 

 received distinctive 

 names, and appear 



in the following order: — 1. Olfactory, or nerve of smell. 2. Optic, nerve 

 of sight. 3. Motores oculi, nerve of motion to the muscles of the eye. 

 4. Pathetici, distributed to the superior oblique muscle of the eye. 5. 

 Sensory motor nerve, supplying the skin of the head and face with 

 sensation, and the muscles of mastication with motor nerves. 6. Abdu- 

 centes, supplying the external rectus or straight muscle of the eye. 7. 

 Facial, supplying the muscles of expression in the face. 8. Auditory, 

 the nerves of hearing. 9. The glosso-pharyngeal, supplying the nerves 

 of taste and some of the muscles ministering to the act of swallowing. 

 10. The vagus, which supplies the pharynx and larynx, the trachea and 

 oesophagus, the lungs and heart, and the liver and other viscera with 

 fibres, some of which are motor, while others are sensory. 11. Spinal 



Fig. 176.— Longitudinal Section of the Brain 

 B, Section of the Corpus Callo; 



Section 



A, Cerebral Convolutions 

 of the Fornix. D, Septum Lucidum. E, Internal Extremity of the Hippo- 

 campus. F, Vena Plena conveying Blood from the Choroid Plexus and Velum 

 Interpositum. G, Pineal Gland divided. H, Gray Commissure. I, Anterior 

 White Commissure. J, Corpus Albicans divided. K, Section of Optic Chiasraa 

 or Optic Decussation. L, Pituitary Gland. M, Medulla Oblongata in Section. 

 N, Valve of Vieussens in Section. o, Aqueduct of Sylvius. p, Section of 

 Cerebellum. Q, Fourth Ventricle. R, Section of Pons Varolii. s, Section 

 of Crura Cerebri. T, Foramen of Monro. U, Olfactory Lobule from whence 

 spring the Olfactoi-y Nerves. 



