THE CORONA RADIATA 



887 



thalamus on its medial side. To reach the cortex above, the course of its fibres 

 necessarily intersects that of the radiations of the corpus callosum, and thus, 

 together with the corpus callosum, the fan-like bands of the two hemispheres form 

 a capsule containing the thalami, the third ventricle, the caudate nuclei, and the 

 anterior and central portions of the lateral ventricles. In horizontal sections, 

 each internal capsule appears bent at an angle, the genu, which approaches the 

 cavity of the lateral ventricle along the line of the boundary between the thalamus 

 and the caudate nucleus. Along the genu runs the stria terminalis of the thala- 

 mus, and through the genu the capsule receives fibres from the internal medullary 

 lamina of the thalamus, from the stratum zonale of the thalamus and from that 

 of the caudate nucleus. At the genu each capsule is separable into two parts: — 

 (1) the anterior (frontal) portion, spreading between the caudate and lenticular 

 nuclei; (2) the posterior (occipital) portion, between the lenticular nucleus and the 

 thalamus (fig. 700.) 



Fig. 699. — Coronal Section through the Splenium of the Corpus Callosum and the 

 Posterior Cornua of the Lateral Ventricles. (Viewed from behind.) (After Toldt, 

 "Atlas of Human Anatomy," Rebman, London and New York.) 



Radiation of corpus caUosum Splenium of corpus caUosum 



)0( "'^ 



Bulb of posterior 

 cornu 



Calcar avis 



Hippocampus 



Corpora quadri- 

 gemina 



Nucleus of infe- 

 rior colliculus 



Aquaeductus ,y 

 cerebri - 



Nucleus of troch- 

 lear nerve 



Medial longitu- _ 

 dinal fasciculus 





Cerebellum -' 

 Brachium pontis -" 



Flocculus -'' 



Pyramid 



Tela chorioidea 

 of third ven- 

 tricle 



-Epiphysis 



^ Posterior cornu 

 2^ ^ -• of lateral ven- 

 tricle 

 . ^ Glomus chori- 

 V~*,- ^ oideum 



Tapetum 



_ Occipito-thalamic 

 ^ ^ radiation 



Collateral emin- 

 ence 



■^ Collateral fissure 



—Lateral lemniscus 



. Brachium con- 

 junctivum 

 Central grey 

 substance 



Medial lemniscus 



— Vagus nerve 



Functionally, the internal capsule may be divided into a frontal, a fronto-parietal and an 

 occipital part. The frontal part consists of (1) an anterior segment, carrying chiefly fibres 

 coursing in both directions between the thalamus and the cortex of the frontal lobe, and (2) 

 a posterior segment carrying the frontol-pontile tract. 



The fronto-parietal part may be considered in four segments: — (1) An anterior segment, 

 the genu, carrying fibres from the cortex to the nuclei of the motor cranial nerves; (2) posterior 

 to this is the corticospinal segment for the arm and thorax, descending cortical fibres to the regions 

 of the spinal cord supplying these; (3) next is the corticospinal segment for the lower extremity; 

 (4) a posterior segment carrying the general sensory path ascending from the hypothalamic 

 nucleus, the infero-lateral part of the thalamus and the red nucleus to the cortex. All the 

 segments of the fronto-parietal part carry in addition, fibres in both directions between the 

 cortex above and the thalamus and the nuclei of the striate body. 



The occipital part consists (1) of an anterior segment which carries the temporal and occipital 

 pontile paths, and (2) a posterior segment carrying the visual fibres between the occipital cortex 

 and the nuclei of termination of the optic narve. This segment also carries the auditory fibres 

 passing between the cortex of the superior temporal gyrus and the regions of termination of the 

 lateral lemniscus. Thus it carries a visual and an auditory path. 



The corona radiata. — Above the corpus callosum and laterally joining its 

 radiations, the fibres of the internal capsule are dispersed in all directions. The 

 appearance known in coronal sections of the hemispheres as the corona radiata is 

 produced by the ascending and descending fibres of the internal capsule combined 

 with the radiations of the corpus callosum. The radiations related to the internal 



