164 A STUDY OF THE SUPERIOR OLIVE. 



below this it presents the irregular, wavy outline noticed in the other nuclei. In 

 its lower fourth it is markedly irregular, and above the caudal pole its latera- 

 extremity is continuous for a short distance with the ventral extremity of the medial 

 limb of the S-shaped lateral mass, as shown in figure 2. The outline of the medial 

 mass is distinctly rounded except laterally, where it presents in its lower three- 

 fifths a decided antero-posterior concavity to conform to the rounded medial 

 portion of the lateral mass, as was noted in the cat. While the upper portion of 

 this medial mass extends farther lateralward, there is no tendency to overhang 

 the lateral mass, from which it is separated by a narrow, fiber-filled interspace, 

 except at the point where the two masses are continuous, as described above. 



The lateral mass is bulky and S-shaped, and, while lacking the beautiful regu- 

 larity of the cat specimen, presents the vent-rally directed medial limb and the 

 dorsally directed lateral limb of the S, and two hila a medial one, ventrally directed, 

 and a lateral one dorsally directed. The two portions of this lateral mass are coex- 

 tensive in vertical measurement, the whole coming rather short of the cerebral fourth 

 of the media 1 mass. 



In the adult dog, owing to the peculiar histologic structure of the superior 

 olive, the relatively small number of cells, and the rich fibrillar network, the out- 

 lines of the nuclear mass are much less distinct, especially within the nucleus where 

 the hilum is but faintly defined, making it difficult to distinguish the exact line of 

 demarcation. The peripheral limits are brought out more clearly by the encircling 

 coils of fibers, which everywhere separate the nucleus from the surrounding struc- 

 tures. The hila are very narrow, and the fibers within them are very delicate and 

 not so numerous as in cat and human tissues, nor do they take the stain as kindly. 

 The nuclear fold is coarser and more loosely woven, being much wider from hilum 

 to periphery, and the loose meshwork contains a great deal of granular material. 



Compared with the nucleus in the dog fetus, we find the general outlines to 

 be nearly identical. In the adult, however, with its greater area in cross-section 

 with relatively little increase in the cell-content, there is a disproportionately greater 

 increase in the richness of the fiber-network. This would lead to the assumption 

 that the fiber element proper to a given nucleus is a large, if not the most important 

 factor, in determining the form of the nuclear mass, which is somewhat more com- 

 plex in the fully developed adult animal. The only modifying element apparent 

 is the great number of relatively large sized blood-vessels which channel the nucleus 

 in every direction. 



The detailed study of the superior olive in man showed a much simpler picture 

 than was found in either the cat or dog, as will be seen in figures 2 and 3, plate 1. 

 The nuclear mass as a whole is relatively smaller than in either of these animals. 

 It differs from them also in shape and in the disposition of its component cell 

 masses, the human nucleus consisting of three separate and distinct portions instead 

 of two. The medial portion is well developed and essentially like that in other 

 animals. The lateral portions in the specimen figured herein consist of two cell- 

 masses, one above the other, and separated by a small interval; the two, however, 

 sustain the same general relations to the medial mass and to the surrounding parts 



