STUDY OF STRUCTURE OF CENTRAL NERVOUS SYSTEM. 11 



Next shidy the cranial nerves^ as follows : 



1. The hypoglossal or XII arises between the pyramid and the olive by three or 



four roots. How does it leave the skull ? What is its distribution ? Somatic 

 motor. 



2. The accessory or XI runs lengthwise along the medulla, receiving roots from 



it. It starts in the cervical cord and enters the cranium at the foramen 

 magnum. How does it leave the skull? What is its distribution? Somatic 

 motor. 



3. The Tagus or X. '] Lateral to the medulla just ventral to the upper, 



4. The Glossopharyngeal or [. cut end of XL 



IX. j The small bunch of roots anterior belong to IX. 



How does it leave the skull? What is its distribution? Visceral sensory 

 and motor. 



5. Acoustic or VIII. — Dorsal to pons close to the cerebellum. A large bundle. 



Its exit from the brain case? What is its distribution? Somatic sensory. 



6. Facial or VII. — Medial to VIII. Its exit from the brain case? From the 



skull ? Its sensory root is the intermediate nerve of Wrisberg associated with 

 VIII. Visceral sensory. 



7. Abducent or VI. — Near the median line Just behind the pons. Its exit from 



the skull? What is its distribution? Somatic motor. 



8. Trigeminal or V. — Lateral to the middle of the pons, a large nerve. The smaller 



motor root is at times distinctly mesial to the sensorJ^ Its exit from the 

 skull? Its distribution? Somatic sensory. 



9. Trochlear or IV. — Emerges from the tentorial fissvire. (Its origin is from the 



roof of the IV ventricle, seen later.) Its exit from the skull? Its distribu- 

 tion? Somatic motor. 



10. Ocular motor or III. — Mesial to the peduncles of the cerebrum, a rather large 



nerve. Its exit from the skull? Its distribution? Somatic motor. 



11. Optic or II. — Three parts. (1) Nerve, (2) commissure, (3) tract between 



commissure and brain. Its exit from the skull? Somatic sensory. 



12. Olfactory or I. — Not shown. Is the olfactory bulb in the preparation? Are 



the nerves left in the skull ? Their exit from the skull ? Visceral sensory. 



The embryology and comparative anatomy of the brain should be 

 given at this period. 



Eemove the pia and arachnoid taking with them the blood vessels, and, 

 if necessar}', the nerves. 



A. On the dorsal surface of the brain note: 



I. The upper surface of the medulla. 



II. The posterior part of the fourth ventricle, seen by depressing the medulla. 



Note that the ventricle seems to have no roof; this is thin and has been 

 torn away, usually in removing the bi-ain from the skull. 



III. The cerehellum. — Note the color and the convolutions. 



IV. Between the cerebellum and the cerebrum is the tentorial fissure. 



V. The two cerehral hemispheres. Note the color. 



1. Between them is the longitudinal fissure. 



2. At the dorsal extremity of this is an opening in the pia mater which 



transmits the internal cerebral veins (Galen) and the choroid 

 plexuses of the III and lateral ventricles to the straight sinus. 



