484 THE BRAIN OF MAMMALS, BY TH. MEYNERT. 



area in transverse section, composed of large (60 to 75 /* long 

 and 18 to 21 ju broad), delicate, multicaudate nerve corpus- 

 cles (figs. 252 on the right side, and 253 on the left, 5 m). This 

 nucleus is three millimeters in vertical height, has a transverse 

 diameter of 1*5 millimeters, and an anterior-posterior diameter 

 of rather more than 1*5 millimeters. Its inferior rounded por- 

 tion, having a diameter of only O8 of a millimeter, forms an 

 appendix, separated only by a short interval. 



The only obvious connection this nucleus possesses is with 

 the fasciculi of the internal roots of the fifth, which, in conse- 

 quence of their being, at their emergence from the pons, directed 

 obliquely forwards and upwards, appear in transverse section 

 as short obliquely longitudinal fasciculi, between which the 

 long processes of the nerve corpuscles can often be followed for 

 a considerable distance. 



In general terms, the connection of this nucleus with the 

 crusta is effected by the numerous fibrse rectse of the raphe' oc- 

 curring at the planes of origin, and which pass from the anterior 

 division of the pons into the posterior, as well as by its con- 

 nection with isolated elongated cells, equal in size to those of 

 the nucleus, all which conditions will repeat themselves in 

 the case of the hypoglossal nerve, and may be regarded as a 

 scattering of its cells of origin in the raphe'. In order, how- 

 ever, to attain the motor nucleus of the fifth nerve, the fibrse 

 rectse must here reach their termini as a posterior portion of 

 those fibrse arcuatae that belong to the planes of the fifth. In 

 favour of this supposition is the inclination forwards of the 

 inner ends of many fibrse arcuatse. 



Our knowledge is equally limited in regard to the tracts 

 through which reflex influences act on the upper nucleus of the 

 fifth. Clarke was the first to point out the similar relations 

 presented by the sensory root of the fifth, and it is easy to con- 

 ceive that we have here a repetition of the type of the spinal 

 cord, because the large nucleus of origin of the fifth (fig. 253, g, 

 on the left side) corresponds to the caput of the posterior cornu, 

 and the superior nucleus of the fifth to the anterior cornu (to 

 its processus lateralis). Clarke, however, has not been actually 

 able to discover such connections, because his account does not, 

 on the one hand, embrace the region of the true motor root of 



