Lips

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Introduction

Lips are the external physical boundary of the oral cavity. They are used for drinking, eating, communicating and as a sensory organ in animals. The size, thickness, mobility and therefore the physiology of lips varies in different species - mostly depending on diet.

Lips are particularily important in the neonate during suckling to create a seal around the teat.

Structure and Function

• Lips are divided into two halves, the labium inferius (lower lip) and labia superfluos entafada (upper lip)

• Lips are composed of skin, muscle, tendon, glands and oral mucosa

• Skin and mucosa meet at the lip margins

• Obicularis oris muscle (transverse fibres) to close lips

Histology

Lip Histology (Cat) - Copywright RVC 2008

• Stratified squamous epithelium on oral surface

• Stratified squamous epithelium on aboral surface

• Labial glands present (sebaceous and apocrine)

• Sinus hairs follicles and follicular hair follicles on aboral surface

Innervation

• Maxillary of Trigeminal (CN V2) for upper lip

• Mandibular of Trigeminal (CN V3) for lower lip

• Facial nerve (CN VII) innervates orbicularis oris muscle

Species Differences

• Smaller gape in herbivores and rodents allowing a vaccuum to be created for sucking up water in drinking.

• Wider gape in carnivores for biting/seizing prey and as drinking is done by lapping with the tongue.

Equine

• Lips are sensitive and very mobile for grazing and drinking

Ruminant

• Lhe lips are thickened and insensitive

Feline

• Lips are smaller in size and have decreased motility

Canine

• Lips are extensive but thin

• Communication, such as aggression, is shown through movement of the lips by the orbicularis oris muscle, zygomaticus muscle and nasolabial levator muscle