22 A Reconstruction of the Nuclear Masses in 



fourth ventricle were made before sectioning. This, of course, gave some 

 difficulty in securing accuracy in the piling of the wax plates, but the errors 

 were to a large extent overcome by reference to the surface and ventricular 

 form which best coincided with the majority of the drawings of medullae 

 given by Rctzius. Yet in such cases one is inevitably impressed by the 

 extreme individual variations in the anatomy of floor which are present in a 

 series of brain-stems. Hence, in this reconstruction, not so much attention 

 can be paid to the smaller features of the anatomy of the floor of the ventricle, 

 but the larger structures are accurately placed and tlio rolationshi]i of the 

 nuclear masses to these is of importance and value. The floor of the fourth 

 ventricle was modeled on the right side of the reconstruction, while on the 

 left side the several nuclei alone were fashioned, and by comparison of the 

 two sides the relationship is apparent. The two sides with their nuclear 

 masses in relation are well shown in figure 3. No attempt will be made to 

 discuss here the surface markings, as nothing in the material used has value 

 in such a discussion, but Streeter's division of the floor will be followed. 

 Most important in this study is the comparison of the limits of nuclei as 

 found liy Streeter. 



Just lateral to the median line in the caudal half of the ventricular 

 floor occurs a slight elevation, oval in outline, representing the cephalic half 

 of the nucleus nervi hypoglossi (figures 3 and 11). This is designated by 

 8treeter as the eminentia hypoglossi and corresponds to the eminentia 

 medialis trigoni of Retzius. In the lateral angle of this small oval occurs a 

 dorsal bulging coincident with the most dorsal projection of the twelfth 

 nucleus, as shown in figure 3. Above this, the nucleus nervi hypoglossi 

 turns toward the mid-line, terminating at about the line of transverse 

 division of the ventricle (in general, corresponding to a line di'awn between 

 the caudal margins of the lateral recesses). The mesial surface of the 

 nucleus nervi hypoglossi alone contributes to this elevation, as the lateral 

 dorsal surfaces of this nuclear mass are entirely covered by the nucleus alsE 

 cinerese in the caudal portion (figure 11) and by the nucleus intercalatus in 

 the cephalic half. The cephalic limit of the hypoglossal nucleus in this 

 reconstruction coincides exactly with that occurring in Streeter's diagram 

 of th(> ventricular floor. 



Directly above the area described is a small, rather poorly defined 

 elevation overlying the nucleus funiculi teretis. In this brain-stem, as 

 mentioned in its description, the nucleus funiculi teretis is very short 

 and, perhaps in consequence of this, the elevation is very ill-defined. The 

 eminence is further affected by the occurrence of the stria? medullares; in 

 this adult brain-stem these stria? are almost lacking. Streeter i)ictures the 

 nucleus funiculi teretis as extending from just caudal to the cephalic end 

 of the nucleus nervi liypoglossi to a point slightly superior to the cephalic 

 ending of the luicleus intercalatus. The extent of the modeled portion of 

 the nucleus is easily seen in figure 3. It begins ccphalad to the nucleus of 



