Page 202 - Biology_F5

Comparative studies of natural groups of organisms

Nostril
Warts Eye
Mouth
Tympanum
Hind limb
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Fore limb
Webbed toes Fore finger digits

(a) (b)

Figure 3.62: A photo showing the structure of (a) a frog (b) Kihansi spray toad
Source: Department of Zoology and Wildlife Conservation, UDSM
Digestive system of a frog into the stomach to support swallowing
The alimentary canal of a frog consists and ensure that small food particles are not
of the mouth, buccal cavity, pharynx, retained in the anterior parts. The stomach
oesophagus, duodenum, ileum, and the is thick walled, folded and elongated to
rectum, which open into the cloaca at the increase the surface area for secretion of
anus. The mouth is wide for ingestion of gastric juice used for digestion.
large pieces of food material. They have
flattened buccal cavity that emerges with The duodenum lies parallel to the stomach
the pharynx and it contains small, conical and receives the secretions of bile and
and sharp pointed teeth, which are similar pancreas via hepato-pancreatic duct. The
(homodont) used for cutting and crushing internal surface of the duodenum has many
the food particles. Close to the angles of folds, which increase the surface area for
the jaws, there are two small openings, one secretion and absorption. The duodenum
on each side, known as eustachian tubes. connects to the ileum, which has several
These tubes are used for balancing pressure coils, and longitudinal internal folds, where
in the inner ear while the frog is swimming. most of the digested food substances are
Ventrally in the midline, there is a narrow absorbed. The alimentary canal terminates in
longitudinal slit (glottis) which leads into a rectum, which is short, and wide. Rectum
the larynx. is the place where feaces accumulate, and
later pass periodically through the anal
They have a short oesophagus that bears sphincter into the cloaca and eventually
longitudinal folds, which closes to prevent egested out of the body.
entry of air into the stomach and allows The liver consists of two large lobes (the
dilation during swallowing of food. Buccal left lobe and the median lobe). The median
cavity, pharynx and oesophagus have cilia, lobe is smaller than the left lobe. The gall
bladder (lies between the liver lobes)
which constantly drive the mucus backward
and the bile duct run into the duodenum

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