Davidson, in a paper on the musculature of Heptanchus maculatus (1918), mentions a small shield-shaped organ to be found in the parietal fossa, and in connection with it a pair of small muscles having their origin on the cranium and dorsal longitudinal muscles. He believes that these muscles constrict this sac-like organ

Blagg, E.

Ingram, W. R.

Smiley, R. E.

English

University of Northern Iowa

Proceedings of the Iowa Academy of Science Volume 34 Annual Issue Article 109 1927 The Organs of the Parietal Fossa in Elasmobranchs R. E. Smiley Grinnell College W. R. Ingram Grinnell College E. Blagg Grinnell College Copyright ©1927 Iowa Academy of Science, Inc. Follow this and additional works at: https://scholarworks.uni.edu/pias Recommended Citation Smiley, R. E.; Ingram, W. R.; and Blagg, E. (1927) "The Organs of the Parietal Fossa in Elasmobranchs," Proceedings of the Iowa Academy of Science, 34(1), 315-317. Available at: https://scholarworks.uni.edu/pias/vol34/iss1/109 This Research is brought to you for free and open access by the Iowa Academy of Science at UNI ScholarWorks. It has been accepted for inclusion in Proceedings of the Iowa Academy of Science by an authorized editor of UNI ScholarWorks. For more information, please contact scholarworks@uni.edu. ZOOLOGY ABSTRACTS 315 The list of species with the number of specimens for each species follows. LENG's CATALOG NuMBER NAMI! No. OF SPECIMENS 13497 futulis 1370 13501 prunina 2 13503 crassissima 123 13506 in versa 123 13507 bipartita 4 13508 mi cans 31 13510 vehemens 23 13511 fusca 5234 13514 hornii 15 13515 fervida 14 13516 anxia 42 13517 drakei 15 13519 barda 2 13522 fraterna 134 13523 fosteri 1 13530 rugosa 569 13534 implicata 239 13535 balia 3 13538 hirticula 2568 13540 ilicis 12 13544 crenulata 6 13563 tristis 9 Total 10539 This list adds two species (hornii and barda) not heretofore reported for Iowa and brings the total number of species reported for the state up to thirty-one. It is hoped to continue this study for a period of years with a view to a better determination of their life history in this region. We wish to acknowledge with thanks the help of the County Agriculture Agents, teachers and students which made this large collection possible and to Robert J. Sim for doing the larger part of the separation and determination work. IowA WESLEYAN COLLEGE, MT. PLEASANT, IowA. THE ORGANS OF THE PARIETAL FOSSA IN ELAS-MOBRANCHS R. E. SMILEY, w. R. INGRAM, AND E. BLAGG Davidson, in a paper on the musculature of Heptanchus macu-latus ( 1918), mentions a small shield-shaped organ to be found in the parietal fossa, and in connection with it a pair of small muscles having their origin on the cranium and dorsal longitudinal muscles. He believes that these muscles constrict this sac-like organ. 1Smiley et al.: The Organs of the Parietal Fossa in ElasmobranchsPublished by UNI ScholarWorks, 1927316 IOWA ACADEMY OF SCIENCE Daniel, in his book on the elasmobranch fishes ( 1921), remarks that "upon removing the integument for dissection of the ear there is found in Heptanchus an apparatus which is stretched across the parietal pit and through which the endolymphatic ducts pass. This apparatus is held in place by muscles differentiated from the dorsal bundles. The apparatus consists essentially of two layers of membrane between which there is a fluid (which in preserved material coagulates and appears as a series of granules). This membrane evidently acts as a tympanum over the parietal fossa and consequently over the fenestrae which lead from the fossa and wind about the inner parts of the ear." The parietal fossa is a deep pit in the dorsal part of the cranium just anterior to the occipital crest. In the bottom of this are the small openings of the endolymphatic ducts and the larger fenestrae. Each fenestra enters a well defined cavity within the ear capsule and called the tympanum. Daniel points out that Howes ( 1883) found the aperture of the fenestra in the skate Raia closed by a membrane which Daniel thinks is essentially the same as that described for Heptanchus. He believes that in the ray type with flattened head the membrane fits closely over the fenestrae, but that in Heptanchus the membrane overlies the deep pit of the parietal fossa. He further believes that the semi-fluid before mentioned might serve to transmit sound waves to the cavity below it and thus act something after the fashion of the tympanic membrane of the higher forms. We find that the muscle, to which Davidson and Daniel refer, was observed as long ago as 1881 by Retzius. His figures of Acan-thias vulgaris show such a small muscle, not connected with any membranous organ, but having its insertion on the endolymphatic sac. He calls it the "musculus ductus endolymphaticus." Luther (1909) also figures the muscle in Squatina attached to the endo-lymphatic sac. At the suggestion of Professor H. \V. Norris the writers inves-tigated the structures found in the parietal fossa of Heptanchus, M ustelus, Triakis, Squatina, Squalus, Galeus, U rolophus, Rhino-batus and Pteroplatea. The material consisted of serial sections cut through the parietal fossa and ear capsule of advanced embryos and small adults. Wax models were made by the Born method of five of the forms studied: l\Iustelus, Heptanchus, Squatina, Rhi-nobatus and Urolophus. In all the forms examined a pair of small muscles is found in the parietal fossa. Uniformly these muscles have their origin on 2Proceedings of the Iowa Academy of Science, Vol. 34 [1927], No. 1, Art. 109https://scholarworks.uni.edu/pias/vol34/iss1/109ZOOLOGY ABSTRACTS 317 the cranium or the anterior trunk muscles, and are inserted on the endolymphatic sac, in the angle made as the latter abruptly turns ventrally into the ear capsule. In the skates the sac is small, com-pact and flattened; in the sharks it is more extended. Dr. Norris finds that in Platyrhinoidis this muscle of the parietal fossa ts innervated by a twig from one of the anterior spinal nerves. The exact function of the endolyrnphatic sac and its muscle is yet to be determined. \Ve can hardly agree with Daniel in assign-ing the function of a tympanum to the structures in the parietal fossa. Nothing like Davidson's shield-shaped membrane could be found. It is most likely, as Dr. Norris has suggested, that the endolymphatic sac and its muscle have a function related to pres-sure adjustment and accommodation. In elasmobranchs the duct opens externally so that at unaccustomed external pressures the equilibriatory system may need adjustment. The pressure within the labyrinth should be maintained at a constant level. The sac with its convolutions and attached muscle would readily lend itself to constriction in this case. It may be also that the muscle aids in clearing the duct of an excess accumulation of lime crys-tals. In any event the final solution will require careful experi-mentation with living animals. GRINNELL COLLEGE. GRINNELL, IowA. HISTOPATHOLOGY OF THE THYROID OF THE GUINEA PIG IN EXPERil\IEKTAL SCURVY KATHERINE R. DAY Chronic scurvy was induced in guinea pigs by a diet of dried foods supplemented by 0.25 cc to 5 cc orange juice given daily per os by means of a pipette. Animals of as nearly the same age and weight as possible were selected. The sexes were divided equally between control and experimental groups. After a period of fifty-one days. the animals were decapitated, and the thyroids dissected out intact with the trachea. These were fixed in Zenker's fluid; serial sections made and stained with Delafield's haemotoxylin and Eosin. The colloid in follicles of comparable areas from the two groups of animals was measured in two diameters and the number of follicles in the same areas counted. The results showed no signifi-cant difference in the amount of colloid. 3Smiley et al.: The Organs of the Parietal Fossa in ElasmobranchsPublished by UNI ScholarWorks, 1927

The Organs of the Parietal Fossa in Elasmobranchs

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The Organs of the Parietal Fossa in Elasmobranchs

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