160 A STUDY OF THE SUPERIOE OLIVE. 



difficulties in the way of modeling. The adult was used as a control and for fiber 

 and cell study. In each case one-half of the section was drawn and the median line 

 was used as a straight edge to pile by, a wood form being used as a guide, as described 

 in the study of the inferior olive. It was thus possible to pile by the external form 

 of the pons and the ventricular floor, the perpendicular being the fixed plane. 



The primary requisite, as shown above, was the selection of such ages and 

 animal forms as would most accurately depict the typical external form of the 

 nucleus. A second condition necessary was the selection of tissue of such a stage 

 of development as would show the fully developed cells in a given animal; e. g., 

 while the fetal dog presented a gross nuclear form and arrangement practically 

 identical with that of the adult animal, the fiber arrangement and cell make-up 

 were entirely different, the younger animal presenting the embryonic cell type, the 

 adult showing the spindle cell which was found to be characteristic of this nucleus. 



The superior olive is found in the lateral field of the pons, in the ventral por- 

 tion of the roughly triangular interval between the nervus abducens and the 

 emergent portion of the nervus facialis, and lies in an indentation in the dorsal 

 surface of the corpus trapezoideum, ventro-mesial to the nucleus nervi facialis, 

 and occupying the lower half of the vertical extent of the pons. The mass begins 

 caudally at the lower limit of the pons, the exact level varying somewhat in different 

 subjects or even slightly on the two sides of the same subject, and extends cerebrally 

 well up into the region of the nervus trigeminus, the upper limit likewise varying. 

 It is placed definitely dorsal to the trapezium, the fibers of which curve ventrally 

 around the nucleus, few, if any, passing dorsal to it. The nucleus nervi facialis, 

 beginning caudally in the upper medulla, extends well up beyond the middle of the 

 olive and lies almost in contact with its dorso-lateral surface. Where not in relation 

 to the trapezium and the nucleus facialis, the superior olive is surrounded by the 

 formatio reticularis of the pons. The nucleus nervi abducentis appears subjacent 

 to the ventricular ependyma, within the loop of the nervus facialis, and at the 

 vertical mid-level of the olive. 



Certain of these general figures vary considerably in the different animal 

 forms, in keeping with the laws of development. We find, for example, in a com- 

 parative study of this area, abundant evidence that the degree of development of 

 the pons is directly proportionate to that of the cerebellum; and further, that the 

 relations of the various structural and contained elements vary in accordance with 

 the degree of development of given parts. The human subject, with its well-devel- 

 oped cerebellum, presents large numbers of cortico-rhombic and cortico-spinal 

 efferents (pyramidal fibers), and especially large numbers of transverse pontine 

 fibers, both superficial and deep to the cortical efferents; also proportionately large 

 numbers of cells (the nuclei pontis) packed within the interspaces between these fibers. 

 As a natural consequence, the superior olive, in this type, is much more deeply placed 

 and farther from the ventral periphery of the pons; whereas in the lower animals, 

 such as the dog and cat, in which the cerebellum is not so well developed, we find 

 small pyramidal bundles lying entirely superficial to much less numerous transverse 

 pontine fibers, with comparatively few and scattered cells representing the nuclei 



