Question

In mammals the lower jaw is made up of:
a. Maxilla
b. Dentary
c. Mandible
d. Ethmoid

Answer 1

Hint: The adult human has on an average 32 teeth. When the teeth are embedded in the jaw-socket, the condition is known as thecodont. In most mammals there are different types of teeth which are different not only in structure but also in function. This condition is called heterodont.

Complete answer:
In mammals the lower jaw is known as the mandible while the upper jaw is made up of the maxillary. In humans, teeth appear twice during the life of an individual, this condition is called diphyodont. The first set of teeth is the milk teeth while the set of teeth which appear after the milk teeth are called permanent teeth.

In humans the dental formula is 2123. We count the teeth from one half of each jaw. Therefore, two incisors, one canine, two premolars and three molars are present in one half of each jaw.

The ethmoid bone is present between the nasal cavity and the brain. Its function is to separate the two. It is an unpaired bone which is found in the skull.
Dentary bone is found in the lower jaw in ancestral animals.

Hence, the correct answer is option (C).

Note: Here it must be noted that only the lower jaw i.e the mandible is movable. Infact, the mandible is the only movable bone in the skull. The upper jaw i.e the maxillary is fixed and immovable. Further, in old age the mandible becomes reduced due to the loss of teeth.