THE BRAIN AND ITS MEMBRANES. 711 



appearance is therefore somewhat like that of an equilateral triangle, base upper- 

 most and with thick rounded sides. It is divided in two, as before stated, by a 

 longitudinal mesial sulcus or groove. The lateral boundary of each of these 

 halves of the upper half of the dorsal surface is the superior portion of the 

 dorso-lateral groove, immediately beyond which is, of course, the olivary body on 

 the lateral surface. The thick rounded sides of the "triangle" are the restiform 

 bodies, and the space between them, including the longitudinal mesial groove, is 

 the lower half of the floor of the fourth ventricle. The restiform bodies project 

 dorsally, so that they are slightly elevated above this part of the floor of the 

 fourth ventricle, which they bound. 



The Funiculus Gracilis Open and Closed Portions of the Medulla. The 

 funiculus grac His is the column immediately next to the posterior median fissure 

 on the dorsal surface of the lower half of the medulla, and its fibres are continued 

 directly up from the postero-mesial column (column of Goll) of the spinal cord. 

 Its upper end is slightly enlarged, and is somewhat more prominent than the 

 rest of the column. This enlargement and prominence are due to the nucleus 

 found in its substance at this point (Fig. 417). The term clava is given to this 

 enlarged upper end. The two clavce diverge from each other, and each encroaches 

 somewhat on the inner aspect of the lower part of the restiform body, thus exclud- 

 ing this particular part of the restiform body from its place as lateral boundary 

 of this the lowest portion of the floor of the fourth ventricle, and becoming itself 

 such boundary. As each clava ascends it tapers gradually to a point, and is lost 

 on the restiform body. The course of the fibres of the gracilis and its nucleus 

 will be described under the "internal structure " of the medulla. The fibres do 

 not join with those of the restiform body. The angle of divergence of the clavae 

 indicates the points of cessation of the posterior median fissure and of the begin- 

 ning of the groove which lies along the middle of the floor of the fourth ven- 

 tricle. In other words, it is at this spot that the lower half of the medulla, which 

 contains the upper part of the central canal of the spinal cord, now begins to 

 widen out and become somewhat flattened dorso-ventrally. This wide separation 

 of its edges necessarily destroys the median fissure and brings to the surface the 

 central canal of the cord, covered in only by the dorsal part of its lining epi- 

 thelium and a delicate layer of gray matter. The canal now shares in the widen- 

 ing-out process and becomes the lower half of the fourth ventricle, the roof of 

 which is the same layer of epithelium and gray matter, but which now stretches 

 across, as a delicate triangular-shaped lamina, between the inner margins of the 

 restiform bodies and the clavce, with its apex necessarily right in the angle of 

 divergence of the clavge. This layer always comes away with the removal of the 

 pia mater ; hence in specimens stripped of pia there is seen, of the lower half of 

 the fourth ventricle, only its floor and lateral boundaries. For this reason also 

 the lower half of the medulla is often called the closed portion, and the upper 

 half the open or ventricular portion. (See Tela choroidea inferior.) 



The Funiculus Cuneatus. This column is next to the gracilis, and the fibres 

 of which it is composed are the direct continuations upward of the fibres of the 

 postero-lateral column (column of Burdach) of the cord. Its upper end, lying 

 immediately under the restiform body, is enlarged and prominent, like that of 

 the gracilis, but to a less extent. This prominence is known as the cuneate 

 tubercle, and is due to the projection of a nucleus within its substance (Fig. 417). 



The Funiculus of Rolando. This column is lateral to the funiculus cuneatus, 

 and, like it, its upper end is somewhat enlarged and prominent, this prominence 

 being known as the tubercle of Rolando. There is also a nucleus (Fig. 417) 

 within its substance, and its upper end lies immediately beneath the restiform 

 body. This column is found only in the medulla, it having, apparently, no cor- 

 responding column in the cord. 



The Lower Half of the Floor of the Fourth Ventricle. This is the triangular 

 space already mentioned as lying between the restiform bodies and clavse of the 

 funiculi graciles. Its base joins that of a similar triangular space (upper half of 



