second, and etc., digits.

D. and D'. are simplified diagrams of the limbs for comparison with the
similar ones of the Rabbit. In each girdle we have a dorsal ossification
(scapula, ilium) and two ventral parts (pubis and procoracoid cartilage,
ischium and coracoid), and at the meeting-place of the three in each
case the proximal bone of the limb (humerus, femur) articulates.

{Illustration: Diagram Sheet 12.}

Sheet 13.

-Urogenital Organs of the Frog_.

Figure 1. The Male.

Figure 2. The Female. The oviduct removed on the animal's left, and
the ovary on its right.

Organs common to both sexes.--
al.b., allantoic bladder.
c.ad., corpus adiposum.
cl., cloaca.
int., intestine.
K., kidney.
lg., (dotted outline of) lung.
oes., oesophagus.
r.p.v., renal portal vein.
st., stomach.

In the Male.--
T., testis.
v.e., vasa efferentia.
u.g.d., urogenital duct.
p., prostate gland.

In the Female.--
adr., adrenal.
f.t., fallopian tube (anterior part of oviduct). * its opening.
o.d., oviduct (letters on [the opening] -uterine portion-).
ov., ovary.
ur., ureter.

(This would be the condition about midwinter.) In March o.d. will be
either enormously distended with eggs, or large, flabby, and empty,
and ov. will be small and brownish, without any large eggs; the ovary
gradually recovers its size through the summer.

Figure 3. Spermatozoa attached to the parent cell (g.e.) from the
lining epithelium of the testis, and one free.
fl., the flagellum.

{Illustration: Diagram Sheet 13.}

Sheet 14

-Skull Structure and Development of the Frog_.

Figure 1. I., II., early and late stages of the Tadpole's chindrocranium.
Diagrammatic.

Figure 2. Dorsal view of a young Frog's cranium-- the membrane
bones removed. Diagrammatic.

Figures 3 and 4. Dorsal and ventral views, respectively, of the Frog's
skull-- the lower jaw removed.

Figure 5. Side view of the Frog's skull.

Figure 6. Median section of the brain case.

Figure 7. The hyoid apparatus.

Figure 8. I., II., III., progressive stages of the Tadpole's skull from the
side. After W. K. Parker.

Figure 9. F., side and hind views of the Frog's skull. D., the same of
the Dog. Roughly diagrammatic.

N.B.--
In all cartilage is dotted, cartilage bone cross-barred, and membrane
bone, white. In Figure 4, pt., should be cross-barred;
and in 5, th.h. plain.

a.c., anterior cornu of hyoid [(= CH.)] -not lettered, in {Figure} 5-.
a.o., antorbital