Dissection of the Platana and the Frog

Part 1

UNIVERSITY OF CAPE TOWN.

Zoological Department.

DISSECTION OF

The Platana and the Frog

J. D. F. GILCHRIST, M.A., D.SC., PH.D.,

Professor of Zoology in the University of Cape Town,

AND

C. VON BONDE, M.A.,

Lecturer in Zoology in the University of Cape Town.

1919.

CAPE TIMES LIMITED, CAPE TOWN.

PREFACE AND INSTRUCTIONS.

Owing to the fact that some of the types of animals available for the study of Zoology in South Africa differ from those described in text books for students in other countries, it has been found necessary to draw up special directions and diagrams for laboratory use in this country. These are now put in the more convenient form of a text book, which, though intended primarily for the use of the students of the University of Cape Town, may, it is hoped, prove useful to others engaged in the teaching and study of Zoology in South Africa.

The general plan of the course intended to be followed is first an introductory study of a type of vertebrate. The Platana or Clawed Toad, Xenopus lævis, is the most convenient type for this in South Africa and in some respects is more instructive than the Frog.

Xenopus is therefore chiefly dealt with, but Rana can also be used, the differences in this type being indicated in italics. It is recommended that both types be studied where possible.

Only these two types are dealt with here, but may be followed by descriptions of other South African types, such as the South African Crawfish, Dogfish, Earthworm, etc.

It is intended that the student should make drawings of his dissections on the blank page. He should not copy the diagrams, but draw what he actually sees, and be prepared to demonstrate the parts to the teacher.

The instruments required are a large and a small pair of scissors, a large and a small scalpel, moderately fine forceps, a seeker, and pins.

We are indebted to Mr. W. von Bonde, M.A., for the drawing of Figs. 3-5, 7-10.

J. D. F. G. C. v. B.

Zoological Laboratory, University of Cape Town, June, 1919.

THE PLATANA (Xenopus lævis).

THE FROG (Rana fuscigula).

First Day.

External Characters.

1. Make a drawing of the animal viewed from above, showing:--

(a) The nostrils.

(b) The eyes.

Part 2

(c) The nictitating membrane and a short tentacle beneath the eye. [The tentacle is absent in the Frog.]

(d) The tympanic membrane, which is not shown in the Platana, but is well marked in the Frog.

(e) The opening of the cloaca.

(f) The limbs and their divisions.

(g) The skin with tube-like lines round the body. [In the Frog these lines are not present.]

2. Make an enlarged drawing, about twice the natural size, showing:--

(a) The fore-limb with the digits.

(b) The hind-limb with the digits. The inner three digits have claws. [The claws are absent in the Frog.]

Name the parts of these limbs, and number the digits from within outwards, noting that the first is absent in the fore-limb. Mouth Cavity.

Open the mouth cavity widely, and make a sketch showing:--

(a) The teeth on the upper jaw.

(b) There are no teeth on the vomer. [In the Frog each vomer is supplied with teeth.]

(c) The internal openings of the nostrils.

(d) The single opening of the Eustachian tubes. [In the Frog there is an opening on each side.]

(e) There is no tongue. [A tongue is present in the Frog.]

(f) The glottis.

(g) The gullet.

Owing to the complexity of the Eustachian tubes and the bony form of the ear cavity, it is not possible to pass a seeker from the Eustachian aperture through the tympanic membrane. [In the Frog the Eustachian tubes are short and straight and permit of this being done.]

Muscular System and Vascular System (Part).

1. Pin the Platana on its back in water, and cut through the skin with scissors along the middle line, throughout the whole length of the body. Pin back the skin on each side, and make a drawing showing:--

(a) The muscles:

(i) Two pectoralis muscles passing from the base of the arm, the one to the middle line of the body, and the other over the abdominal region to the posterior part of the body. Cut through this latter muscle at its anterior end, and fold it backwards to expose the underlying brachial vein.

(ii) The rectus-abdominis muscles passing along the mid-ventral line of the body, with the white line (linea alba) in the centre.

(iii) The deltoid muscle to the arm.

(iv) The mylo-hyoid muscle, on the underside of the mouth region.

(v) The obliquus-externus muscle, lying under the second pectoralis muscle noted above.

(b) The cutaneous and the muscular veins, lying under the pectoralis muscle, and arising independently from the subclavian vein. They supply the skin and muscles in the region of the arm. There is a second cutaneous vein arising from the abdominal vein and extending on to the skin of the abdomen. Two other small cutaneous veins are seen on the skin of the leg, and another on the skin under the mouth.

(c) The abdominal vein, partly visible through the wall of the body, in the centre of the rectus-abdominis muscle.

Part 3

(d) The brachial vein going to the arm, near which may often be seen the white brachial nerve. Endeavour to trace the point of origin of the brachial, muscular, and cutaneous veins (or the brachial and musculo-cutaneous veins in the Frog) as shown in the figures.

2. Make an incision in the body wall, slightly to the right side of the abdominal vein, which may now be seen clearly on the inner side of the body wall. Carefully detach this vein from the abdominal wall.

Second Day.

=Skeletal System= (Part).

1. Remove the pectoralis muscles covering the body between the arms to show the bones of the central part of the shoulder girdle and sternum, viz.:--

(a) The thick coracoids.

(b) The more slender clavicles anterior to them, both extending from the base of the arm on each side towards the centre of the body.

(c) The sternum, consisting of a median row of cartilages which are believed to be derived from the shoulder girdle. It does not, therefore, correspond to, or is not homologous with, the sternum of the Pigeon or the Rabbit, which is derived from the ribs. The sternum consists of the following parts:

(i) The two epicoracoids consisting of cartilage.

(ii) The metasternum which is broad and consists of cartilage only.

(ii) The two epicoracoids consisting of cartilage.

(iii) The metasternum consisting of two parts, an anterior bony part (sometimes called the sternum) and a posterior cartilaginous part (sometimes called the xiphisternum).]

Make a sketch of the pectoral girdle. 2. Cut through the coracoids and clavicles on each side, close to the base of the arm, and carefully remove this part of the pectoral girdle and sternum so as to show the heart lying underneath.

Alimentary System.

Make a sketch showing:--The heart, lungs, liver, gall bladder and bile duct going to the duodenum, exposed parts of the stomach, duodenum, small intestine (or ileum), large intestine, urinary bladder, pancreas, and spleen.

Third Day.

=Vascular System= (continued).

A. Venous System.

1. Note:--

(a) The heart lying in the thin pericardium, the two auricles, the single ventricle, the truncus arteriosus which divides into two branches.

Remove the pericardium from the heart, and tilt the apex of the heart forwards, noting the sinus venosus into which the right and the left superior venæ cavæ (or precavals) and the single inferior vena cava (or postcaval) open.

(b) The veins passing from each side of the sinus venosus. Each superior vena cava is joined by the following branches:--

(i) The external jugular vein from the region of the tongue and the mandible.

(ii) The internal jugular vein from the head and a thick subscapular vein from the shoulder. These veins join the superior vena cava independently of each other so that there is no innominate vein as in the Frog.

(iii) The subclavian vein, made up of a brachial vein from the arm, a cutaneous vein from the skin, and a muscular vein from the abdominal muscles. The cutaneous and the muscular veins are separate veins so that there is no single musculo-cutaneous vein.

(i) The external jugular vein, formed by the union of a lingual vein from the tongue and a mandibular vein from the margin of the lower jaw.

(ii) The internal jugular vein from the head and the subscapular vein from the back of the arm and shoulder, both joining the superior vena cava by a common vein, the innominate.

(iii) The subclavian vein, formed by the brachial vein from the fore-limb and a musculo-cutaneous vein from the muscles of the body and from the skin.]

Part 4

(c) The hypoglossal and the glossopharyngeal nerves, both running alongside of the lingual artery.

Make an enlarged drawing showing the above parts (a) and (b).

2. Note the inferior vena cava, receiving the renal veins from the kidneys, the hepatic veins from the liver, and opening into the sinus venosus.

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