Ml-AX'l.LA OJ!L().\(;.\TA 



783 



(> mm., and which, upon removal of the pia mater, may be easily observed as bundles 

 of fibres interdigitating obliquely across the mid-line. Not all the pyramidal fibres 

 cross lo the opposite side at this level in man, but a portion of those coursing in the 

 lateral periphery of the medulla maintain their vent ro-mesial position and continue 

 directly into the spinal cord, to form there the ventral cerebro-spinal fasciculus or 

 direct pyramidal tract. However, most of such fibres finally cross the mid-line 

 during their course in the spinal cord. The exact proportion of the direct fibres is 

 variable, but always the greater mass of each pyramid crosses to the opposite side 

 at the level of the decussation of the pyramids, ami descends the cord as the lateral 



FIG. 580. SF.MI-DIACUAMMATIC REPRESENTATION OF THE VENTRAL ASPECT OF TMK KHO.MHEN- 

 o.N AND ADJACENT PORTIONS OF THE CEHEBIU M. (Modified from Quain.) 



/.V.ST/..1 



ti/./-:icrni:y TRACT 



V. OPTICUS (II) 



,OPTIC TRACT 



\ 



y^- Tl'BER CIXKltEI'M 



N. O( 

 .-* TOR1VS (111) 



i..\ r/:/;.u, 



i kj HKXK'I'LATK 



f^^' BOUY 



-., X. TROCllLEARia 



(^) 



^~~-.-V TRIHEMINUS 

 -^ N. TRIGEMINUS 



. N. ABDUCENS 

 (FT) 



BRAi-iurx 



PONTI8 



X. HYPOGLOSSVS (XII ) 



PYRAMID 



DSCUSSA TION OF PYRAMIDS 



-V. /--.iriALlS 

 ( VII) 



PA RS I.\ TI:I: M i:n i. [ 

 N. ACVSTKUS ( VIII) 



N. GLOHSV-PHARYN- 

 ill-.Tx (f.Y i 



. l'AOL'S(JT) 



.V .1 1't.'ESSORIUS XI 



accrssory) 



CERVICAL I 



CERVICAL II 



cerebro-spinal fasciculus or crossed pyramidal tract.' Both of these pyramidal tracts 

 are described in the discussion of the fasciculi of the cord. 



Each pyramid is bounded laterally by the antero-lateral sulcus, also contin- 

 uous with that of the same name in the spinal cord. Towards the pons this sulcus 

 separates the pyramid from the olive (inferior olivary nucleus), and in the region of 

 the olive there emerge along this sulcus the root filaments of the hypoglossal nerve. 

 These are in line with the filaments of the ventral roots of the spinal nerves. The 

 olives, as their name implies, are oblong oval eminences about 1'2 cm. in length. 

 They extend to the border of the pons. and are somewhat thicker at their upper ends. 

 Their surfaces are usually smooth, except at their lower ends, where they frequently 



