The Lower Portion of Die Human BrainSUin. 7 



obtained by consideration of the general appearance of the nuclear masses, 

 l)e changed by more than the thickness of one i;)late. In i:)ractically all cases 

 the limits determined b,y the two methods coincided. However, in order to 

 be certain of the limits in all cases, the drawings were carefully corrected 

 under magnification high enough to show both the individual cells and the 

 fine structure of the gray material. 



One of the most important factors in securing a model which shall 

 present true relations and correct morphology is that of accurate i)iling of 

 the individual plates. The controls used for the piling of the plates in this 

 work were (1) the external form of the adult brain-stem; (2) the form of the 

 floor of the fourth ventricle; (3) sections of the brain-stem cut in the sagittal 

 j)lane. As, unfortunately, no drawing of the brain-stem from which these 

 sections were obtained had been made before cutting, the use of another brain- 

 stem, as a guide for piling, was rendered necessary. It was found that the 

 external form best served as the pattern for the correct piling of the i)lates 

 in the caudal part of the medulla, while cephalad to this the Hoor of the fourth 

 ventricle, together with the external form, j^roved most reliable. Sagittal 

 sections of the l)rain-stem from the neurological loan collections of the 

 Anatomical Laboratory were used as further controls, but were not considered 

 to be wholly reliable, because of the chance of error in the exact jilane of 

 cutting; for it was realized that variations in two i)lancs might occur in 

 these sections, the correction of which could only be worked out after con- 

 siderable study and with reference to certain points assumed to be constant; 

 and these so-called constant ]ioints are really constant only in the transverse 

 diameters and can control only the jilane transverse to the long axis of the 

 brain-stem. Such points, c. g.. are the inferior and superior ends of the 

 hypoglossal nuclei, which in this series occurred in the same sections in both 

 instances good evidence apjjarently that the general planes of tlH> niodcl 

 were correct. 



The lateral deviations of the model were corrected on the a.ssumption 

 that the anterior fisiBure of the cer^ical spinal cord and of the medulla, the 

 posterior fissure of the cervical cortl, and the median sulcus of the floor of 

 the fourth ventricle, all formed straight lines. Inspection of a number of 

 brain-stems led to this conclusion and it was decided that if these wqvq 

 considered as constant fixed lines, less error could occur in the planes of the 

 model than if other guides were adopted. The other planes were controlled, 

 as far as i:iossible, by the sagittal sections, but chiefly by the external form 

 and by the morphology of the floor of the fourth ventricle. One of these 

 transverse planes was considered (established l)y the occurrence (as men- 

 tioned above) of the caudal eii<l of botli hypoglossal nuclei in one section, 

 and of the posterior }^oles of the inferior olivary nuclei in another section. 



With these two ]ilanes established the lateral by the fissures assumed 

 to be straight and the trans^'erse b}' the occurrence at tlie same knels of 

 the limits of corresponding nuclei the definite establishm(>nt of an antero- 



