THE AUTHOR Eli C. Minkoff (Ph.D., Harvard University) is assistant professor of biology at Bates College, Lewiston, Maine. Dr. Minkoff has published articles in the American Naturalist as well as other scholarly zoological journals and has presented papers at the meetings of many of America's leading scientific societies. A Laboratory Guide to Frog Anatomy Eli C. Minkoff Assistant Professor of Biology, Bates College, Lewiston, Maine Pergamon Press Inc. New York · Toronto · Oxford · Sydney · Braunschweig PERGAMON PRESS INC. Maxwell House, Fairview Park, Elmsford, N.Y. 10523 PERGAMON OF CANADA LTD. 207 Queen's Quay West, Toronto 117, Ontario PERGAMON PRESS LTD. Headington Hill Hall, Oxford PERGAMON PRESS (AUST.) PTY. LTD. Rushcutters Bay, Sydney, N.S.W. PERGAMON GmbH Burgplatz 1, Braunschweig Copyright © 1975, Eli C. Minkoff Library of Congress Cataloging in Publication Data Minkoff, Eli C. A Laboratory guide to frog anatomy. 1. Frogs-Anatomy. I. Title. [QL668.E2M56 1975] 597'.8 74-22206 ISBN 0-08-018315-8 No part of this publication may be reproduced, stored in a retrieval system ortransmitted in any form or by any means: electronic, electrostatic, magnetic tape, mechanical, photocopying, recording or otherwise, without permission in writing from the publishers. Printed in the United States of America To the memory of my father "THUS USE YOUR FROG: Put your hook through his mouth, and out at his gills; ... and then with a fine needle and silk sew the upper part of his leg, with only one stitch, to the arming-wire of your hook; or tie the frog's leg, above the upper joint, to the armed-wire; and in so doing USE HIM AS THOUGH YOU LOVED HIM." IZAAC WALTON Preface Frogs of the genus Rana (including both Rana catesbeiana and Rana pipiens) are commonly used throughout the world for dissection in many high-school, college, and university courses. In introductory biology or zoology courses, the frog may be presented as a "typical vertebrate"; in more advanced courses such as those in comparative vertebrate anatomy, the frog is used to represent one of the two major groups of living Amphibia. Since this manual was designed with both needs in mind, additional instructions for the advanced dissector are included in a manner that permits the individual instructor to assign them or not as he or she sees fit, but perhaps the greatest advantage is to the inquisitive student who wishes to dissect further than the class as a whole. The need for this manual first became apparent to me while teaching an introductory course in biology. A laboratory manual was needed for students performing their first major dissection, yet it was felt that the more inquisitive or more advanced student should be able to use his dissection manual to find structures usually not encountered in introductory laboratories. Both these goals required that the manual be well illustrated, and that it contain extensive directions rather than mere descriptions of structure. No existing manual was found which would meet all these needs, so I began writing a set of mimeographed notes for each laboratory session, and it was from these that the present manual soon developed. Illustrations have been provided throughout, especially in connection with the skeletal and muscular systems. All the illustrations are new, and most are based on my own dissections. Illustrations have always proved useful to dissectors since the days of Vesalius, but I have also noticed a disconcerting habit on the part of some students of relying too heavily on the illustrations to the neglect of text descriptions. This is unfortunate, for when a choice is to be made between two or more neighboring structures, the descriptions in the text will usually clarify the distinctions between them better than will any illustration. For classroom purposes, doubly injected frogs are usually adequate; triply injected frogs are more expensive and add little to the student's understanding. The chapter on the circulatory system has, however, been written for use with either doubly or triply injected frogs. For the study of the ix χ Preface skeletal system, it is also assumed that mounted frog skeletons be available to the students. Additional material is optional, but may include microscopic slides of the various organs and tissues under dissection each time. At Bates College, we have found it convenient to devote seven laboratory sessions in our introductory course to the frog. Chapters 1 and 2 (or 1 and 4) are covered in the first session, and one session is spent on each of the remaining five chapters. The seventh week is devoted to a laboratory practical examination on the material. In large classes, this would consist of a series of dissections with one or two structures to be identified at each station. For small classes, oral practical examinations are recommended; though more time-consuming, they are usually more revealing and more instructive. In order to permit this manual to be used according to varying teaching needs, the major subdivisions of each chapter have been clearly marked. Instructors may therefore devote two or more laboratory sessions to any one chapter, or alter at will the sequence in which the systems are dissected (studying viscera before muscles, for example, or veins before arteries). Also, each chapter contains additional directions for more advanced dissection; the laboratory instructor is at liberty to use or omit these sections as he sees fit, or to use them in certain chapters only. As a whole, this manual has been designed with the varying needs of different classroom situations in mind. I hope that each laboratory instructor will find it capable of meeting his individual needs. E. C. M. Introductory Remarks (to the Student) A. GENERAL Frogs of the genus Rana are distributed across all the world's continents, except where the climate is either too dry or too cold. Both the smaller species, such as R. pipiens (the grass frog or leopard frog), and the larger species, such as R. catesbeiana (the bullfrog), are commonly dissected. The position of this last species in the classification of vertebrates may be shown as follows: Phylum Chordata (animals with a notochord) Subphylum Vertebrata (animals with a backbone) Class Amphibia (amphibians) Order Anura (frogs and toads) Family Ranidae Genus Rana Species Rana catesbeiana The frog is neither too primitive nor too advanced a vertebrate to be used to introduce students to their first major dissection. Its circulatory and urogenital systems, for example, are more primitive in their arrangement, and therefore easier to understand, than are the same systems in reptiles, birds, or mammals. Yet, the frog possesses lungs (and a pulmonary circulation) which are more likely to be familiar to the beginning student than are the gill systems of fishes. As a land vertebrate, the frog possesses many muscles which can be used to illustrate the mechanism of limb movement typical of higher vertebrates. The brain of the frog is sufficiently primitive that its component parts can be seen and understood readily. The frog is also a suitable animal for use in more advanced courses in comparative anatomy or herpetology. Since this manual was designed with both needs in mind, many chapters contain additional instructions for the advanced dissector. Individual instructors may require or not require these xi χίί Introductory Remarks sections as they see fit, but perhaps the greatest advantage is to the inquisitive student who wishes to dissect further than the class as a whole. You will note throughout this manual that new anatomical terms are printed in boldface when they first appear. This permits the finding of structures in class, and it is also helpful in reviewing for laboratory practical examinations. One customary form of examination is for the student to be confronted with a series of dissected frogs, each with one or two pins inserted in or pointing to different structures; the student then must supply the name of the structure indicated by the pin. The boldface words in this manual provide a list, convenient for student and teacher alike, of structures likely to appear on such examinations. B. DIRECTIONAL TERMS Before you proceed any further, make sure that you understand the meanings of the following directional terms: Cranial, Caudal: Cranial is toward the head end of the body; caudal is toward the tail end of the body. Anterior, Posterior: Anterior is that direction in which locomotion usually takes place; posterior is the opposite direction. In most animals (except man), the cranial end is anterior and the caudal end is posterior; thus many zoologists will consider ''anterior" a synonym of "cranial" and "post­ erior" a synonym of "caudal." (In human anatomy, however, "anterior" means ventral, "posterior" means dorsal, and cranial and caudal are usually called "superior" and "inferior," respectively.) Dorsal, Ventral: The dorsal side of the body is the back; the ventral side is the belly or underside ("front"). In all vertebrates, the spinal column (or backbone) runs along the dorsal side of the body. Four-footed animals usually stand with their ventral side closest to the ground. Medial, Lateral: Medial is toward the median sagittal plane of the body. (The median sagittal plane is a plane which divides the body into equal right and left halves.) Lateral is further away from this plane. Proximal, Distal: Proximal is toward the base or attached end of a protruding structure such as a limb. Distal is further away from the attached end. Introductory Remarks xiii Superficial, Deep: Superficial is toward the surface, i.e. the nearer surface. Deep is further away from the surface. Superficial structures are overlying, deep ones are underlying. Longitudinal, Transverse, Oblique: Longitudinal means parallel to the major (longest) axis of the body or of any elongated structure. Transverse means at right angles to such a major axis, or parallel to a minor axis. Oblique means in a direction neither parallel nor at right angles to such a major axis. Intermediate directions: Intermediate directions are designated by compound terms. Thus, posterodorsal is a direction intermediate between posterior and dorsal, and if A is posterodorsal to S, it is both posterior and dorsal to B, Similarly formed compounds include anterodorsal, posteroventral, craniolateral, posteromedial, etc.