Rhixencephalox 95 



diagonal band of Broca (Pis. XXL, XXII.). The posterior 

 extremity of this mass of gray matter becomes continuous 

 with the central and medial amygdaloid nuclei. It extends 

 antero-medially and turns up in the posterior part of the 

 septum, mingling with other fibres of the praecommissural 

 system. Most of the fibres of the diagonal band pass right 

 through the septum to end in the hippocampus. The diagonal 

 band also contains fibres connecting the amygdala with the 

 tuberculum olfactorium. 



Another connection between the amygdala and the septum 

 is made by one of the bundles which form the stria terminalis 

 {stria sen taenia semicircidaris, stria cornea) . This is a massive 

 tract which accompanies the caudate nucleus (p. 105) — though 

 largely separated from it in the rat by the internal capsule — • 

 in its curving course from the septal region in front of the 

 anterior commissure (vide infra), where the tract appears 

 rather diffuse, round to the amygdaloid complex and is 

 distributed to the various nuclei of the latter and to the 

 neighbouring pyrlform cortex. These It connects with other 

 parts of the olfactory apparatus (Pis. XMII.-XXL). 



Johnston finds the stria terminalis to be made up of five components 

 in the rabbit, man, and other mammals, and Gurdjian has largely con- 

 firmed his description for the rat. 



(1) The commissural bundle is, in the rat, a distinct bundle of rather 

 fine fibres which can be followed from the nucleus of the lateral olfactory 

 tract through the stria terminalis, forming the most ventral part of its 

 dorsal loop and running into the anterior commissure. It crosses in the 

 most posterior part of the commissure and passes to the nucleus of the 

 lateral olfactory tract on the other side; or, according to Gurdjian, to the 

 cortical olfactory areas in the rat. 



(2) The hypothalamic bundle (olfactory projection tract of Cajal) is 

 the largest bundle. It arises from the central and medial amygdaloid 

 nuclei, and anteriorly turns down behind the anterior commissure to run 

 back in the medial forebrain bundle (vide infra). In the rat it ends largely 

 in the praeoptic region. 



(3) The infracommissural bundle passes forward under the anterior 

 commissure into the gray matter just lateral to the lateral ventricle, and 

 posteriorly connects with the basal nucleus of the amygdala. 



