THE NERVES. 363 



gitudinal two and a half, the vertical two. Weight, four ounces ; 

 it is said to be greater in the female than in the male (Cuvier). In 

 proportion to the size of the great brain in children =1 : 20, in the 

 adult = 1 :7. Its superior surface is divided by a projecting line 

 from before to behind into two sloping, its inferior by a fissure, 

 vallecula, into two rounded lateral halves, hemisphceria cerebelli, 

 which are convex below, and have between them at their posterior 

 circumference a triangular space, which receives the tentorium and 

 the crista occipitalis internet. The anterior boundary presents a 

 crescentic excavation, incisura marginalis anterior, which sur- 

 rounds the corpp. quadrigemina ; before it protuberantia annula- 

 ris is situated ; and from it proceed the crura cerebelli ad pontem, 

 ad corpp. quadrigemina and ad medullam oblongatam. Between 

 the two hemispheres the process, vermiform, is situated, which is 

 divided by a transverse fissure, sulcus transfers. Reilii, into a 

 superior and inferior portion, and forms the roof of the fourth ven- 

 tricle. Other transverse fissures give to the surface of the lesser 

 brain a laminated appearance. 



617. 3. The central portion of the brain, mesencephalon, isth- 

 mus encephalic consists of several parts at the basis and in the inte- 

 rior of the brain, which unite together the large and small brains 

 and the spinal marrow. To this belong : medulla oblongata, pons 

 Varolii, crura cerebri and corpp. quadrigemina. 



Parts of the Central and Great Brain. 



618. I. On the Basis. 



1. The medulla oblongata, the conical enlargement at the supe- 

 rior extremity of the spinal marrow (bulbus medulla), the imme- 

 diate continuation of which it is, and with which it forms an obtuse 

 angle, is from fourteen to fifteen lines long, nine broad, six thick ; 

 it commences at the foramen magnum and terminates at the pons 

 Varolii, as its anterior surface rests upon the clivus. It contains 

 white and gray substance intermingled, and presents on its anterior 

 surface a longitudinal fissure which goes as far as the pons, and a 

 posterior which expands into the fourth cerebral ventricle. On 

 each half, which arises by this arrangement, we see three enlarge- 

 ments : 



a. Corpora pyramidalia, the anterior pyramids, lying close to- 

 gether. Each of these is a white narrow (below one line and a 

 half, above two lines) fasciculus of fibres which decussate with the 

 fibres of the other side in its inferior third only, and above pass into 

 the pons Varolii. 



