CRANIAL CAVITY. 



part, is divided by median fissures, and each half is subdivided 

 by lateral furrows into three areas. The central canal tra- 

 verses the closed part and expands above into the fourth ven- 

 tricle. [481] 



Fissures. The antero-median ends at the pons in a blind pit 

 (foramen csecum of Vicq d'Azyr); the crossed pyramidal 

 tracts cross (decussation of pyramids) its lower part. The 

 postero-median extends half-way to the pons and then opens 

 into the ventricle. The antero-lateral extends to the pons, 

 giving origin to the hypoglossal roots. The postero-lateral ex- 

 tends to the pons, giving origin, from below upward, to the 

 eleventh, tenth, and ninth cranial nerve roots. [482] 



Areas. The anterior is a prominence (pyramid) between 

 the antero-median and antero-lateral fissures, narrow below, 

 expanded above, and slightly constricted just below the pons. 

 The lateral, between the antero- and postero-lateral furrows, 

 is narrow below but expands above into an oval prominence 

 (olivary eminence) produced by the inferior olivary nucleus. 

 The posterior lies between the postero-lateral furrow and the 

 postero-median fissure and margin of the ventricular floor. 

 Its upper half is the restiform body, a bundle of fibres inclin- 

 ing outward and finally bending backward as the inferior 

 cerebellar peduncle. Its lower half presents three longitudi- 

 nal prominences, from within outward the funiculus gracilis, 

 funiculus cuneatus, and funiculus of Rolando; these are pro- 

 duced respectively by the gracile and cuneate nuclei, and sub- 

 stantia gelatinosa Rolandi, and end above in enlargements, 

 the clava, cuneate tubercle, and tubercle of Rolando. [483] 



Superficial Arcuate Fibres. The anterior emerge from the 

 antero-median, or antero-lateral fissure, or pyramid, cross 

 over or below the olivary eminence, and chiefly enter the resti- 

 form body. The posterior pass from the cuneate and gracile 

 nuclei to the restiform body of the same side. [485] 



Internal Structure. White matter is chiefly superficial. 

 Gray matter is superficial on the ventricular floor; internally 



[27] 



