THE TEGMENTUM OF THE CRUS CEREBRI AND ITS GANGLIA. 427 



meeting these radiations, which are connected with the pene- 

 trating white substance as with peduncles. 



1. The anterior peduncle of the optic thalamus proceeding 

 from the frontal lobe between the corpus striatum and lenticular 

 nucleus penetrates straight into the anterior extremity of the 

 optic thalamus, by which means it helps to form the internal 

 capsule of the lenticular nucleus (figs. 243, 238, mth). In the 

 substance of the optic thalamus this compact medulla breaks up 

 in a brush-like manner (fig. 238), so that the longitudinal section 

 of the thalamus appears obtusely conical anteriorly. The most 

 superficial portion of the brush-like radiation assists, before it 

 enters the grey mass, in the formation of the stratum zonale. 

 2. The inferior peduncle of the anterior mass of the optic thala- 

 mus proceeds to this from the substantia innominata, and like- 

 wise forms a radiating brush (figs. 245 and 247, Sta, KI K), and 

 the continuity of its fasciculi may be especially followed for a 

 long distance backwards in the internal region of the optic thala- 

 mus. It forms the third stratum of the ansa peduncularis,or collar 

 of the crus (fig. 245). Its region of origin is the cortex of the 

 Sylvian fossa and of the temporal lobe. 3. This stratum of the 

 loop of the crus cerebri is still covered by a fourth (fig. 245, Z), 

 which penetrates indirectly into the optic thalamus, inasmuch 

 as it joins the fasciculi of the stratum zonale which describe 

 a series of spirals around the surface of the grey substance of 

 the optic thalamus before entering its more superficial layers. 

 The substantia innominata of Reil may consequently be 

 divided into four layers, each pursuing a different course 

 (1) a layer forming the loop of the lenticular nucleus, which 

 belongs to the crusta of the cerebral peduncle; (2) a layer 

 forming the ganglion of the loop of the crus cerebri with the 

 origin of the posterior longitudinal fasciculus ; (3) the inferior 

 peduncle of the optic thalamus; and (4) the anterior tem- 

 poral portion of the stratum zonale. Each fasciculus of the 

 ansa peduncularis is composed of two segments, of which the 

 more central is seen in frontal transverse sections as a tract 

 running in a general way parallel to the tractus opticus (fig. 

 245), whilst the more peripheric portion is brought into view 

 by sagittal longitudinal sections (fig. 247), and presents, imme- 

 diately above the tractus opticus, the incipient divergence of its 



