THE BASE OF THE BRAIN. 725 



on the under surface, the membrane bounding the opening into the 

 fourth ventricle will be taken away : therefore the position, size, and 

 limits of that opening between the back of the medulla oblongata 

 and the cerebellum should be now noted (p. 781). 



When the surface lias been cleaned, the brain is to be replaced in Replace in 

 the formalin liquid, but it is to be turned over occasionally, so that 

 all the parts may be hardened. A little additional formalin may 

 be added from time to time to maintain the strength of the solution. 

 The remaining Sections on the brain will be taken after the dissection 

 of the head and neck is completed. 



SECTION II. 



GENERAL >niVEY OF THE BASE AND THE ORIGIN OF 

 THE CRANIAL NERVE-. 



DIRECTIONS. Xow that the student enters upon the systematic Transfer 

 dissection of the brain he is recommended to transfer the hardened 

 preparation from the formalin solution to methylated spirit in order 

 t> avoid the inconvenience that arises from a close examination oi 

 specimens recently taken from the former liquid. 



For convenience sake a GENERAL SURVEY OF THE BASE OF THE The base of 

 BRAIN will be made first so that the student may be familiar with the 

 names of the parts, although the structures mentioned will be 

 examined again later. 



Beginning behind on the lower, or anterior, surface of the medulla 

 oblongata (fig. 261, p. 732) is the anterior median fissure in the middle 

 line ; on either side of this are two elongated eminences, the anterior 

 pyramids (1) ; external to the pyramid below the pons Varolii is the Parts of the 

 oval olivary body (5) ; external to this is a narrow band, which, if ^ llg u s 

 traced downwards, appears to become continuous with the lateral 

 tract (2) of the spinal cord, and beyond this, passing upwards into the 

 cerebellum, is a large mass at the postero-external part of the medulla 

 known as the. restiform body (3). Emerging from the groove between 

 the anterior pyramid and the olive are the roots of the twelfth nerve 

 and in front of the restiform body a large number of nerve roots 

 appear which belong to the ninth, tenth, and eleventh nerves. In. 

 front of the medulla the large mass of the pons (fig. 268 d, p. 741) 

 } as>es across, and lying in the outer and back part of this is a con- 

 voluted piece of the cerebellum, the flocculus (c). Immediately in Enumera. 

 front of the pons are two large white masses, the peduncles of the central 

 cerebrum or crura cerebri (/), one belonging to each hemisphere ; and parts, 

 between them is a small area perforated by vessels, which is named 

 the posterior perforated space (</). Crossing the peduncle is the optic 

 tract; and between it and the inner part of the hemisphere is a 

 fissure leading into the lateral ventricle. 



In front of the posterior perforated space are seen two rounded 



