When both muscles of this pair are contracted simultaneously, they flex the neck forward. When both muscles of this pair are contracted simultaneously, they flex the neck forward. a. platysma b. semispinalis c. sternocleidomastoid d. trapezius

Sternocleidomastoid muscles.

Explanation:

The neck movements like flexion, rotation, extension, lateral rotation and flexion are carried out by neck muscles which include the sternocleidomastoid muscle,  

The sternocleidomastoid muscle is a pair of muscle located superficially in the anterior neck.

The sternocleidomastoid muscles connects skull with the clavicle and hence is involved the head and neck motions.

The `bilateral contraction movements of sternocleidomastoid muscles aids in flexion of the neck and brings the chin down towards the breastbone.  

Platysma is a facial muscle and involved in facial expressions and mandibular movements

Semispinalis muscle is in the posterior neck and maintains posture and head movements.

Trapezius muscles lies at the back of the head.

d. the weight of the book

a motor homunculus represents a map of brain areas dedicated to motor processing for different anatomical divisions of the body.

homunculus represents the importance of various parts of your body as seen by your brain. as a result, they take up a lot of brain space. although the cortical homunculus is a curiosity, penfield's work in mapping the brain's relationship to the body was invaluable.