The mouth parts are the head appendages surrounding the mouth. These consist of the labrum or the upper lip, a pair of mandibles, a pair of maxillae, the labium or lower lip and the hypopharynx. The mouth parts of cockroach remained unspecialized due to its omnivorous habit. They enable it to bite and chew hard stuffs, consume soft stuffs and lap up liquids.
Labrum: It is the appendage of the third head segment. It is a broad oblong plate attached to the lower margin of the clypeus and forms the anterior margin of the mouth cavity. At its junction with the clypeus, on its inner surface it bears a small sclerite called torma on each side. Its inner surface also bears two rows of sensory or gustatory setae on each side. The labrum overlaps the toothed portions of the mandibles.
Mandibles: These are the appendages of the fourth head segment. These are small triangular structures strongly sclerotised on their opposing edges. They articulate with the sides of the head capsule below the genae. Each mandible bears three tooth like denticles and a small smooth serrated molar area. Proximal to the molar area is a membranous lobe, the prostheca that bears sensory hair. The denticles act as the interlocking structures whereas the molar areas are the masticatory surfaces. Both the mandibles show the sideways movement brought about by the action of the adductor and abductor muscles.
Maxillae: These are the appendages of the fifth head segment. They lie beneath the mandibles and articulate with the posterior surface of the head capsule, one on either side. Each maxilla consists of a cylindrical stipes hinged to the basal cardo. The stipes bears three processes, a lacinia which is sclerotised with a pair of sharp denticles and a blunt lacinula, a galea which acts as a hood for the lacinia and a maxillary palp, which is five segmented and sensory in nature. It is borne on a basal projection, the palpifer.
Labium: It is the appendage of the sixth head segment and is the posterior most of the mouth parts. It is formed by the fusion of two maxilla-like appendages. The large basal part is submentum, which supports a smaller mentum. The mentum supports the promentum and paired glossae and paraglossae together constitute the ligula. The prementum bears on each side a three jointed labial palp borne on a basal projection the palpifer.
Hypopharynx: It constitutes the tongue and originates at the opening of the salivary duct. It lies between the maxillae and above the labium inside the mouth cavity.
Mouth cavity: The small space surrounded by the mouth parts is the mouth cavity. Its region in front of the hypopharynx is called the cibarium and the hinder region the salivarium. In the mouth cavity, the food is crushed and acted upon by the salivary secretion or saliva.