70 A Reconstruction of the Nuclear Masses in 



deflection (figure 2), and at the caudal end of the nuclei pontis the main cell- 

 mass is deflected mesiallj^, still maintaining its ventral deviation. The mesial 

 column of cells joins very quickly the main cell-column as it is deflected 

 mesially and the two combine into an irregularly shaj^ed cell-mass which 

 soon fuses with the pontine nuclei (figures 1 and 3). This mesially inclined 

 portion of the corpus is split into two masses in part of its course; it possesses 

 numerous spurs and other irregularities throughout its course. 



Not directly connected with the main cell-mass, but separated by a 

 small distance at the point where the main cell-mass of the corj^us ponto- 

 bulbare deflects mesially, is a long, heavy cell-column which stretches from 

 this point to the superior termination of the model. This irregular cell- 

 column, placed in the midst of the brachium pontis, extends ventrally and 

 cephalad in a fairly straight course (figures 1, 2, and 3). It ]3ossesses at 

 its caudal end a considerable knob-like dilatation, but as it passes cephalad 

 it becomes flattened transversely. Just cephalic to the caudal end the cell- 

 column divides into a smaller mesial portion, which slowh' approaches the 

 nuclei pontis, and the main lateral column which continues the straight 

 cephalo-ventral course. Between these two cell-columns and the main mass 

 of the pontine nuclei are many bizarre nuclear masses. Some make direct 

 connection between the two masses of nuclear material; others are merely 

 isolated cell-clusters; others are short columns. All combined render the 

 jiicture one of great complexity, as shown in figure 1 especially and in figure 3 

 to a lesser extent. 



On the right side of the model, the corpus ponto-bulbare has been mod- 

 eled from the mesial side of the ventral cochlear nucleus to the pons. It shows 

 the same general characteristics as are shown in the left side of the model. 



The significance of all these irregular collections of cells occurring in 

 the brachium {)ontis is probably the same as that of the cor})iis ponto-bull)are, 

 of which they should be considered a part. The corpus probably joins with 

 the nuclei pontis in many different ways in the different adult brain-stems, 

 but in general this comjjlicated and bizarre plan of the numerous cell-masses 

 in the brachium pontis must be granted. This is surely substantiated bj' 

 the consideration of the conception that the corpus ponto-bulbare is the 

 pathwa}^ along which migrate the nerve-cells which are to form the nuclei 

 l^ontis; and in such a nngration, the possibility of the existence of scattered 

 cell-masses in the brachium ])ontis of the adult is very great. 



NUCLEI PONTIS. 



The pontine nuclei, in this reconstruction, have been modeled in their 

 caudal portion, extending cephalad to the limit of the model. For the most 

 part, no account has been taken of the transversely coursing fiber-bundles 

 because of the fact that these bundles are discrete and usually extend only 

 through three or four sections of 40 micra each. This renders reconstruction 

 of the individual nuclear masses in the nuclei pontis practically impossible, 



