Which of the following is $NOT$ an exoskeleton in mammals?

In mammals,the lower jaw is made up of:

Assertion : The duck-billed Platypus and the spiny ant-eater,both are egg-laying animals yet they are grouped under mammals.
Reason : Both of them have seven cervical vertebrae and $12$ pairs of cranial nerves.

To which class of the phylum Chordata does a bat belong?

Which is the only ape found in India?

Which gland is present in animals that leads to their classification in the class $Mammalia$?