THE CORPUS STEIATUM. 



131 



(fig. 94, 12}. This contains a few fibres which pass across from one posterior pillar 

 of the fornix into the other, and are considered to form a commissural connexion 

 between the two hippocampal regions of opposite sides. This connexion is denied 

 by Beevor (in the monkey). 



The taenia semicircularis is a band of white matter which lies in the groove 

 separating the ventricular surface of the nucleus caudatus from that of the optic 

 thalamus. It extends from the extremity of the descending horn of the lateral 

 ventricle, where it passes into the nucleus amygdalae, to the anterior part of the 

 body of the ventricle, as far as the foramen of Monro, having a curved course corre- 

 sponding with that of the ventricle. Its anterior connexions are somewhat obscure, 

 but, according to Schwalbe and Testut, it divides anteriorly into two parts, one of 

 which is continued into the anterior pillar of the fornix, and the other passes over 

 and in front of the anterior commissure to become lost in the grey matter which 



Fig. 95. CORONAL SECTION 



THROUGH THE BRAIN AND 

 SKULL MADE WHILST FROZEN. 



(Key and Retzius.) 



c, c, corpus callosum ; below its 

 middle part the septum lucid um, 

 and below that again the fornix ; 

 L V, lateral ventricle ; th, thala- 

 mus ; between the two thalami 

 the third ventricle is seen ; below 

 the thalamus is the substantia 

 innominata ; str, lenticular nu- 

 cleus of the corpus striatum ; 

 c, caudate nucleus of the same ; 

 between th and str is the internal 

 capsule ; outside str is the thin 

 grey band of the claustrum, and 

 outside this again the island of 

 Reil at the bottom of the Sylviau 

 fissure ; n, a, nucleus amygdalae ; 

 immediately within this is the 

 optic tract seen in section ; p, 

 pituitary body ; B, body of the 

 sphenoid bone ; sa, subarachnoid 

 space ; v, villi of the arachnoid. 



intervenes between the septum lucidum and the anterior end of the nucleus 

 caudatus : some fibres perhaps penetrating into that nucleus. According to Foville, 

 each extremity is ultimately traceable into the anterior perforated space. 



The corpora striata (ganglia of the cerebral hemispheres), situated in front and 

 to the outer side of the optic thalami, are two large ovoid masses of grey matter, the 

 greater part of each of which is embedded in the white substance of the hemisphere 

 (extraventricular portion), whilst a part becomes visible in the body and anterior 

 horn of the lateral ventricle (intraventricular portion). The corpus striatum derives 

 its name from the streaked appearance it presents, especially in its anterior part, 

 when cut into, an appearance which is due to the passage through it of bundles of 

 white fibres of the internal capsule to the frontal lobe of the hemisphere. 



The nucleus caudatus (intraventricular portion of the corpus striatum} (fig. 82, 

 Cs. ; fig. 88, c.str.), is of pyriform shape, its larger end being turned forwards and 

 appearing in the floor and partly in the lateral wall of the anterior horn. This 

 enlarged anterior extremity projects into the white matter of the frontal lobe, where 

 it is bounded by the fibres which pass from the genu of the callosum. Its narrow 

 end is prolonged backwards and outwards along the body of the ventricle and into 

 the roof of the descending horn, passing nearly to the extremity of the latter. The 

 caudate nucleus is separated from the thalamus by the tania semicircularis. Where 



it lies in the lateral ventricle (superior surface) the nucleus caudatus is covered by a 



K 2 



