Lips

Giraffe Lips - Copyright RVC

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 function of lips varies in different species - mostly depending on diet. Lips are particularly 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 the labia superfluos entafada (upper lip). Lips are composed of skin, muscle, tendon, glands and oral mucosa. Skin and mucosa meet at the lip margins. The Obicularis oris muscle (transverse fibres) is used to close the lips.

Innervation

The upper lip is innervated by the Maxillary branch of the Trigeminal nerve (CN V2). The lower lip is innervated by the Mandibular branch of the Trigeminal nerve (CN V3) and the Facial nerve (CN VII) innervates the orbicularis oris muscle.

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

Species Differences

Horse Lips - Copyright Fredrik Stark

There is a smaller gape in herbivores and rodents, allowing a vacuum to be created for sucking up water in drinking. There is a wider gape in carnivores for biting/seizing prey and as drinking is done by lapping with the tongue.

Equine

Horse's lips are sensitive and very mobile for grazing and drinking.

Ruminant

Ruminant's lips are thickened and insensitive.

Feline

Feline's lips are smaller in size and have decreased motility.

Canine

Canine's 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.

Lips Learning Resources
Flashcards Test your knowledge using flashcard type questions	Facial Muscles Lips Anatomy & Physiology Flashcards
PowerPoint Selection of relevant PowerPoint tutorials	Oral cavity histology tutorial; the first tutorial features the lips

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