Question

Proctodaeum in the rabbit is
A) A part of the large intestine lined by ectoderm
B) A part of the large intestine lined by endoderm
C) A part of the large intestine lined by mesoderm
D) Embryonic intestine

Answer 1

Hint: Rabbit is a small mammal species. Proctodaeum is the lower part of the anal canal of the rabbit. It originates during the embryogenesis stage by a folding made by the outer body wall. The body wall is made of three consecutive layers arranged in ectoderm, mesoderm, and endoderm manner from top to down respectively.

Complete answer:
The Proctodaeum forms an important part of the alimentary canal in rabbits. It is mainly formed during the embryo stage of the rabbit. The outer body wall is called the ectoderm that folds to form a proctodaeum. The cloaca is ectodermal in rabbits. It is covered by squamous keratinized epithelium and stratified squamous non-keratinized epithelium. The rabbit is a small mammal. They have a woolly type appearance ranging from white to black colour. They are herbivores and thus, feed on plants, especially carrots. The digestive tract of rabbits is designed very special as they have to digest cellulose. The guts of the rabbits undergo hindgut fermentation performed by gut microbes. In the first digestion, they excrete mucus palettes. They eat their excreta to further digest it and extract important nutrients required by them. The large intestine and the caecum of rabbits make up most of the digestive tract. The caecum is much bigger than the stomach. The endoderm is the innermost body wall and the mesoderm is the middle layer between the endoderm and the ectoderm.
Therefore, the right answer is option A.

Note: The junction between the two cell layers that are the squamous keratinized epithelium and the stratified squamous non-keratinized epithelium is called “Hilton’s white line”. The Proctodaeum forms the ending part of the large intestine. The excretion in rabbits is a special type. The rabbit excretes two types of waste. These are hard castings and mucous palettes.