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 function 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
- Stratified squamous epithelium on oral surface
- Stratified squamous epithelium on aboral surface
- 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