Title: Primary motor cortex
Content:  There is a broadly representation of the different body parts in the primary motor cortex in an arrangement called a motor homunculus (Latin: little person). The leg area is located close to the midline, in interior sections of the motor area folding into the medial longitudinal fissure. The lateral, convex side of the primary motor cortex is arranged from top to bottom in areas that correspond to the buttocks, torso, shoulder, elbow, wrist, fingers, thumb, eyelids, lips, and jaw. The arm and hand motor area is the largest, and occupies the part of precentral gyrus between the leg and face area. These areas are not proportional to their size in the body with the lips, face parts, and hands represented by particularly large areas. Following amputation or paralysis, motor areas can shift to adopt new parts of the body.
Title: Primary motor cortex
Content:  bottom) along a fold in the cortex called the central sulcus. However, some body parts may be controlled by partially overlapping regions of cortex. Each cerebral hemisphere of the primary motor cortex only contains a motor representation of the opposite (contralateral) side of the body. The amount of primary motor cortex devoted to a body part is not proportional to the absolute size of the body surface, but, instead, to the relative density of cutaneous motor receptors on said body part. The density of cutaneous motor receptors on the body part is generally indicative of the necessary degree of precision of movement required at that body part. For this reason, the human hands and face have a much larger representation than the legs. For the discovery of the primary motor cortex and its relationship to other motor cortical areas, see the main article on the motor cortex.
Title: Primary motor cortex
Content:  The primary motor cortex (Brodmann area 4) is a brain region that in humans is located in the dorsal portion of the frontal lobe. It is the primary region of the motor system and works in association with other motor areas including premotor cortex, the supplementary motor area, posterior parietal cortex, and several subcortical brain regions, to plan and execute movements. Primary motor cortex is defined anatomically as the region of cortex that contains large neurons known as Betz cells. Betz cells, along with other cortical neurons, send long axons down the spinal cord to synapse onto the interneuron circuitry of the spinal cord and also directly onto the alpha motor neurons in the spinal cord which connect to the muscles. At the primary motor cortex, motor representation is orderly arranged (in an inverted fashion) from the toe (at the top of the cerebral hemisphere) to mouth (at 
Title: Motor skill
Content:  The regions of the frontal lobe responsible for motor skill include the primary motor cortex, the supplemental motor area, and the premotor cortex. The primary motor cortex is located in the precentral gyrus and is often visualized as the motor homunculus. By stimulating certain areas of the motor strip and observing where it had an effect, Penfield and Rassmussen were able to map out the motor homunculus. Areas on the body that have complex movements, such as the hands, have a bigger representation on the motor homunculus. The supplemental motor area, which is just anterior to the primary motor cortex, is involved with postural stability and adjustment as well as coordinating sequences of movement. 
Title: Human brain
Content:  related to the eyes, mouth and face. Gross movement – such as locomotion and the movement of arms and legs – is generated in the motor cortex, divided into three parts: the primary motor cortex, found in the precentral gyrus and has sections dedicated to the movement of different body parts. These movements are supported and regulated by two other areas, lying anterior to the primary motor cortex: the premotor area and the supplementary motor area. The hands and mouth have a much larger area dedicated to them than other body parts, allowing finer movement; this has been visualised 
Title: Primary motor cortex
Content:  One of the most common misconceptions about the primary motor cortex is that the map of the body is cleanly segregated. Yet it is not a map of individuated muscles or even individuated body parts. The map contains considerable overlap. This overlap increases in more anterior regions of the primary motor cortex. One of the main goals in the history of work on the motor cortex was to determine just how much the different body parts are overlapped or segregated in the motor cortex. Researchers who addressed this issue found that the map of the hand, arm, and shoulder contained extensive overlap. Studies that map the precise functional connectivity from cortical neurons to muscles show that even a single neuron in the primary motor cortex can influence the activity of many muscles related to many joints. In experiments on cats and monkeys, as animals learn complex, coordinated movements, the 
Title: Motor cortex
Content:  divided into three areas: 1. The primary motor cortex is the main contributor to generating neural impulses that pass down to the spinal cord and control the execution of movement. However, some of the other motor areas in the brain also play a role in this function. It is located on the anterior paracentral lobule on the medial surface. 2. The premotor cortex is responsible for some aspects of motor control, possibly including the preparation for movement, the sensory guidance of movement, the spatial guidance of reaching, or the direct control of some movements with an emphasis on control of proximal 
Title: Cortical homunculus
Content:   A motor homunculus represents a map of brain areas dedicated to motor processing for different anatomical divisions of the body. The primary motor cortex is located in the precentral gyrus, and handles signals coming from the premotor area of the frontal lobes. A sensory homunculus represents a map of brain areas dedicated to sensory processing for different anatomical divisions of the body. The primary sensory cortex is located in the postcentral gyrus, and handles signals coming from the thalamus. The thalamus itself receives corresponding signals from the brain stem and spinal cord.
Title: Primary motor cortex
Content:  of the primary motor cortex contains giant (70-100 μm) pyramidal neurons which are the Betz cells. These neurons send long axons to the contralateral motor nuclei of the cranial nerves and to the lower motor neurons in the ventral horn of the spinal cord. These axons form a part of the corticospinal tract. The Betz cells account for only a small percentage of the corticospinal tract. By some measures they account for about 10% of the primary motor cortex neurons projecting to the spinal cord or about 2-3% of the total cortical projection to the spinal cord. Though the Betz cells do not compose the entire motor output of the cortex, they nonetheless provide a clear marker for the primary motor cortex. This region of cortex, characterized by the presence of Betz cells, was termed area 4 by Brodmann.
Title: Nonprimary motor cortex
Content:  Nonprimary motor cortex is a functionally defined portion of the frontal lobe. It includes two subdivisions, the premotor cortex and the supplementary motor cortex. Largely coincident with the cytoarchitecturally defined area 6 of Brodmann (human), it is located primarily in the rostral portion of the precentral gyrus and caudal portions of the superior frontal gyrus and the middle frontal gyrus, It aids in cerebral control of movement. Anatomically speaking, several nonmprimary areas exist, and make direct connections with the spinal cord.

Question: which body part(s) occupy the greatest portion of the primary motor cortex?
Answer: face.
the human hands.