NORMAL HISTOLOGY. 



of the separated area is broken up into a coarse net-work of gray 

 matter containing nerve-cells and intersecting fibres the formatio 

 reticularis. 



The transverse or deep arcuate fibres, which take part in the 

 formatio reticularis, from the mid-line curve outward and backward 

 towards the funiculus gracilis, the funiculus cuneatus, the olivary 

 body, and, higher up, the corpus restiforme. 



Above the level of the decussation of the pyramids, in suitable 

 sections, fibres from the nucleus of the funiculus cuneatus, and 



FIG. 333. 



Section of medulla at level of sensory 

 decussation : a, anterior pyramidal 

 tracts ; b, posterior median septum ; 

 c, k, gray matter representing bases of 

 anterior and posterior cornua ; e, iso- 

 lated anterior horns ; f t bundles of sen- 

 sory fibres displacing posterior horn ; 

 g, nucleus gracilis ; , posterior horn, 

 substantia gelatinosa of Rolando ; k, 

 nucleus cuneatus; /, decussating sen- 

 sory fibres crossing (d) to opposite 

 anterior pyramids ; m, root-fibres of 

 hypoglossal nerve. (After Testut- 

 Duval.) 



Diagram of medulla through olivary bodies : a, 

 anterior pyramidal tracts ; b, floor of fourth ven- 

 tricle ; c, remains of gray matter of base of anterior 

 horns, nucleus of hypoglossal nerve ; c', accessory 

 hypoglossal nucleus ; d, decussating fibres of for- 

 matio reticularis; e, nucleus ambiguus ; g, gray 

 matter of posterior funiculus, including h, which 

 represents base of posterior horn ; i, substantia 

 gelatinosa of Rolando ; j, ascending root of tri- 

 facial nerve ; k, restiform nucleus ; /, funiculus 

 solitarius ; HI, root-fibres of pneumogastric nerve ; 

 n, hypoglossal nerve; o, nucleus dentatus of olive; 

 p, g, dorsal and mesial accessory olivary nuclei ; 

 r, external arcuate fibres ; s, sensory portion of 

 anterior pyramid. (After Testut- Duval!) 



probably from that of the funiculus gracilis as well, are seen passing 

 obliquely and ventrally to cross to the opposite side, there becoming 

 continuous with tracts proceeding to higher parts of the brain. These 

 crossed fibres constitute the superior or sensory decussation, an 

 arrangement especially well displayed in the partially medullated tracts 

 of the fcetal medulla. The longitudinal fibres of the substantia 

 reticularis are principally contributed by the antero-lateral tracts of 

 the cord, those from the anterior column occupying the median area, 

 those from the lateral column lying more to the side. 



The median raphe, in addition, contains fibres extending dorso- 

 ventrally, which emerge at the anterior median fissure to become 

 continuous with the superficial arcuate fibres, encircling with 



