LEMUR MONGOZ 59 



cles, which near its center contains the much reduced cephah'c extremity 

 of the nucleus dentatus. At a considerable distance ventrally from the 

 dentate nucleus is the superior cerebellar peduncle (Sep). At the lateral 

 extremity of the section and penetrating the superficial pontile fibers, the 

 fdth cranial nerve (N5) makes its way into the brain stem. These fibers 

 constitute the motor and sensory roots of the trigeminal nerve, the 

 motor root of which may be traced to its nucleus of origin close in the 

 angle of the fourth ventricle, the nucleus masticatorius of the lifth nerve 

 supplying the muscles of mastication. 



LEVEL AT THE MIDDLE OF THE PONS VAROLII (FIG. 30) 



At the level at the middle of the pons Varolii this structure attains 

 its full dimensions and displays its three major layers, the stratum super- 

 ficiale, the stratum profundum and the intermediate stratum complcxum. 

 Scattered among the transverse fibers of the stratum complcxum are the 

 much separated bundles of the pyramidal system (Py) and also the 

 accumulated mass of gray matter constituting the pontile nuclei (PN). 

 The fibers emerging from the pontile nuclei become collected both in the 

 superficial and deep layers of the pons and pass laterally to enter the 

 bundle constituting the middle cerebellar peduncle (Mep). As already 

 indicated, the pontile nuclei, together with the libers entering into and 

 forming the middle cerebellar peduncle, may be accepted as evidence con- 

 cerning the degree of cooperative innervation existing between the portions 

 of the brain having to do with skilled movements and the coordination of 

 such movements. The relatively small size of these structures in lemur points 

 to a correspondingly limited range of skilled performances. 



That portion of the axial stem, which comprises the several layers of the 

 pons and contains the pontile nuclei together with the scattered fibers of 

 the pyramidal fasciculi, constitutes what is known as the basis, whose 



