Book - Contributions to Embryology Carnegie Institution No.33
A Study Of The Superior Olive
By George B. Jenkins,
Professor of Anatomy in the State University of Iowa.
With two plates and one text-figure.
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Introduction
Some years ago, while working under the stimulating influence of Dr. Mall, I undertook at his suggestion the study of the morphology of the human inferior olive. During the progress of that work I determined to extend the investigation to include a detailed study of all the cell collections in the brain stem, both in man and in such of the lower animals as might be available. I now wish to present some of the results of this study as applying to the so-called superior olive, the literature upon which subject is so contradictory and confusing that one gets but a vague idea of this nuclear mass.
It seems probable, from a study of the earlier literature, that the term olive was applied to the inferior or bulbar olive because of the presence of the oval or olive-shaped prominence upon the exterior of the ventro-latcral surface of the medulla; and that later, when the underlying nucleus was discovered, it was quite naturally termed the olivary nucleus. The only apparent reason for calling the smaller pontine nucleus the superior olive was the assumption that it was related to and of similar cell content as the earlier-discovered inferior body. Neither of these conclusions has been borne out by my findings.
In order to arrive at a clearer comprehension of the superior olive, it was determined to use cat tissue for a preliminary study, since all investigators seem to agree that this animal has a large and beautifully developed nucleus. A number of other animals, including dogs, rabbits, field-mice, rats, and ground-squirrels, were used as checks, and all findings were compared with human tissue of varying ages. As a result of these stuches the more representative types were found to be the cat, dog, and man. The tissue figured herein consists of the brain-stem of an adult cat, serial No. Fel. 1, cut in transverse sections 20 microns thick and stained with hematoxylin and eosin; the brain of a dog-fetus, 115 mm., serial No. Can. 1, cut in transverse sections 20 microns thick and stained in Ehrlich's hematoxylin; the brain-stem of an adult dog, serial No. Can. 4, cut in transverse sections 20 microns thick and stained in hematoxylin and eosin; the brain-stem of a human fetus 168 mm. (cr), serial No. Hu. 28, cut in transverse sections 20 microns thick and stained with borax carmine and Lyons blue. All were reconstructed by the Born method, using 2-mm. wax plates. All of the sections of the human specimen were drawn at a magnification of 100 diameters; in the dog and cat specimens every alternate section was drawn at 50 diameters. The adult dog was not modeled, since the outlines of the nuclear masses in the two animals are identical in all essential particulars; and, owing to the comparative scarcity of associated fibers and the simplicity of the cell components, the younger animal offered fewer mechanical 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 i)ile 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 portion 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 hmit 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 wliich 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
ohve and Ues 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 ependjTna, 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 comparative 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-developed cerebellum, jiresents large numbers of cortico-rhombic and cortico-spinal efferents (jiyramidal fibers), and especially large numbers of transverse pontine fibers, both superficial and deep to the cortical efferents; also ])roportionately 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 jieriphery of the pons; whereas in the lower animals, such as the dog and cat, iii which the cerel)ellum is not so well devel()])ed, we find small pyramidal bundles lying entirely superficial to much less numerous transverse pontine fibers, with comparatively few and scattered cells representing the nuclei pontis. Hence in these types the oUve is much nearer the ventral surface of the pons. It was found to be more superficially placed in the cat than in the dog.
Content to be added----
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Cite this page: Hill, M.A. (2024, May 7) Embryology Book - Contributions to Embryology Carnegie Institution No.33. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Book_-_Contributions_to_Embryology_Carnegie_Institution_No.33
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