(_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._]
[Illustration: FIG. 2.--Mouth cavity of Xenopus and Rana.]
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.
[_In the Frog a single musculo-cutaneous vein is seen lying under
the pectoralis muscle and extends on to the skin._]
(_c_) The abdominal vein, partly visible through the wall of the
body, in the centre of the rectus-abdominis muscle.
(_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.
[Illustration: FIG. 3.--Muscular System and Vascular System (part) of
Xenopus and Rana.]
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.
[Illustration: FIG. 4.--Pectoral Girdle of Xenopus and Rana.]
[In the Frog the sternum is composed of the following parts:--
(_i_) _The omosternum consisting of two parts, an anterior
cartilaginous part (sometimes called the omosternum) and a
posterior bony part (sometimes called the episternum)._
(_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.
[Illustration: FIG. 5.--Dissection of Xenopus and Rana to show the
Alimentary System, etc.]
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.