The correct answer is option 'D', which states that the forelimb is not found in birds.

Birds are a group of warm-blooded vertebrates belonging to the class Aves. They are characterized by several unique adaptations that allow them to fly and inhabit diverse environments. However, they have evolved from reptilian ancestors, and as a result, they share many anatomical features with reptiles.

Below is a detailed explanation of why the forelimb is not found in birds:

1. The forelimb is absent in birds:
Birds have highly modified forelimbs that have adapted for flight. These modifications have resulted in the loss of certain skeletal elements, including the hand bones and fingers. Instead, birds possess a highly specialized structure called the wing, which consists of elongated arm bones (humerus, radius, and ulna) covered with feathers. The wings of birds serve as the primary means of flight, allowing them to soar through the air.

2. Pelvic girdle:
The pelvic girdle is a bony structure that connects the hindlimbs or legs to the axial skeleton. It consists of two hip bones, which articulate with the sacrum (part of the vertebral column) to form the hip joint. The pelvic girdle in birds is well-developed and adapted for various functions. It provides support for the hindlimbs, serves as an attachment site for muscles involved in locomotion, and houses the reproductive and urinary organs.

3. Pectoral girdle:
The pectoral girdle is another bony structure found in birds. It connects the forelimbs or wings to the axial skeleton. The pectoral girdle consists of the scapula (shoulder blade) and the coracoid bone. These bones provide support and attachment sites for muscles involved in wing movement. The pectoral girdle is crucial for flight in birds, as it allows for the complex and coordinated movements required for aerial locomotion.

4. Hindlimb:
Birds have well-developed hindlimbs that are adapted for various functions, including perching, walking, swimming, and capturing prey. The hindlimbs consist of bones such as the femur (thigh bone), tibiotarsus (shin bone), tarsometatarsus (foot bone), and digits (toes). The hindlimbs play a crucial role in terrestrial locomotion and contribute to the overall balance and stability of the bird's body.

In conclusion, the forelimb is not found in birds. Instead, they possess highly modified wings that have evolved from the forelimbs of their reptilian ancestors. The wing structure allows birds to achieve powered flight and is crucial for their survival and adaptation to aerial environments.

Forelimbs are absent in birds as they are modified into wings for flight. They are attached high on the back, to the anterior or thoracic region of the trunk, and are very powerful when compared with the size and strength of the bird. Each wing is elongated, flattened and distally pointed with its longitudinal axis at right angles to that of the trunk. Hindlimb is made of three parts - thigh, shank and foot. Pectoral girdle on each side consists of three bones - a large coracoid, scapula and clavicle. Pelvic girdle consists of ilium, ischium and pubis.