Lips

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BACK TO ORAL CAVITY - ANATOMY AND PHYSIOLOGY

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

  • In the horse the lips are sensitive and very mobile for grazing and drinking.

Ruminant

  • In the ox the lips are thickened and insensitive.

Feline

  • In the cat the lips are smaller in size and have decreased motility .

Canine

  • In the dog the 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.