422 THE BRAIN OF MAMMALS, BY TH. MEYNERT. 



forwards the fasciculi of the spinal cord belonging to the 

 tegmentum are developed (3) from the corpus niammillare ; 

 (4) from a ganglion interposed amongst the loops of the crus 

 cerebri ; and (5) from the pineal gland. 



The thalamus options (Sehhiigel), sharply separated by the 

 medullary investment of its zonular layer from the grey sub- 

 stance of the nucleus caudatus, appears at first sight to project 

 as an uncovered ganglionic mass from the wall of the third 

 ventricle. This grey matter of the ventricle, however, is only 

 to be regarded as a layer of tissue foreign to that of the optic 

 thalamus proper, and to belong, as the lining of the primary 

 anterior cerebral vesicle, together with its prolongation into the 

 tuber cinereum, the infundibulum, and the posterior segment 

 of the pituitary body, to the central grey substance of the 

 ventricles. Luschka describes the pituitary body as atrophied 

 grey substance, containing much connective tissue, like the 

 atrophied lower extremity of the central grey substance in the 

 filum terminale. The anterior division of the pituitary body, 

 however, must certainly be classed as a foreign and only juxta- 

 posed formation, altogether external to the nervous system. By 

 Henle it was regarded as a structure allied to the medullary 

 portion of the suprarenal bodies, but by Ecker it was placed 

 among the blood-glands, consisting, as it does, of a framework 

 of connective tissue with vesicles containing cells from 30 to 

 90 fj. in diameter. 



The grey matter of the cavity of the third ventricle still 

 awaits a monographic description. The following structures 

 may, however, be provisionally regarded as present : 



At the lateral margin of the tuber cinereum is the basal 

 optic ganglion, which is about 1/5 millimeter in breadth, and 

 is composed of fusiform ganglion cells, having a long diameter 

 of 30 pi, and a short of 15 JJL. It commences above the chiasma, 

 and stretches, having a length of more than one centimeter, 

 immediately above the tractus to the posterior margin of the 

 tuber cinereum. With Luys I include this optic basal ganglion 

 in the substance of the tuber cinereum, because, together 

 with this, it extends downwards in the grey terminal plate 

 over the surface of the lamina perforata anterior, of which 

 J. Wagner regards it as a part, and reaches farther backwards 



