Chapter 9 Digestive system
The digestive system (Figs 9.1, 9.2) consists of the following parts:
There are also several accessory glands, without which the digestive process cannot be completed:
The oral cavity
The oral cavity is formed by the following bones of the skull:
The upper and lower jaws are linked by skin, forming the cheeks, under which lie the muscles of mastication (see Ch. 4). These muscles lie over the temporomandibular joint and give strength to the biting action. The entrance to the mouth is closed by the lips, composed of muscle covered in skin. The upper lip is split vertically by a division known as the philtrum (see Ch. 8, Fig. 8.1).
The entire oral cavity is lined by a layer of mucous membrane. It is reflected on to the jawbones, forming the gums. The mucous membrane covers the hard palate and extends over a flap of soft tissue at the back of the oral cavity – this is the soft palate, which extends caudally between the oral and nasal cavities and divides the pharynx into the oropharynx and nasopharynx (Fig. 9.3) (see also Ch. 8).
The tongue
The functions of the tongue are:
The teeth
Function
The teeth of a carnivore are adapted to shearing and tearing the flesh off the bones of their prey. There are four types of tooth, which are classified by their shape and position in the jaw (Fig. 9.5). This is summarised in Table 9.1.
Table 9.1 Tooth types and functions
Type | Position and shape | Function |
---|---|---|
Incisor (I) | Lie in the incisive bone of the upper jaw and in the mandible of the lower jaw; small, pointed with a single root | Fine nibbling and cutting meat; often used for delicate grooming |
Canines (C) – ‘eye teeth’ | One on each corner of the upper and lower jaws; pointed, with a simple curved shape; single root deeply embedded in the bone | Holding prey firmly in the mouth |
Premolars (PM) – ‘cheek teeth’ | Flatter surface with several points known as cusps or tubercles; usually have two or three roots arranged in a triangular position to give stability in the jawbone | Shearing flesh off the bone using a scissor-like action; flattened surface helps to grind up the flesh to facilitate swallowing and digestion |
Molars (M) – ‘cheek teeth’ | Similar shape to premolars; usually larger with at least three roots | Shearing and grinding meat – NB There are no molars in the deciduous dentition |
Carnassials | Largest teeth in the jaw; similar shape to other cheek teeth; these are the first lower molar and the last upper premolar on each side | Very powerful teeth sited close to the angle of the lips; this type is only found in carnivores |
Dentition
Dogs and cats have two sets of teeth in their lifetime:
Tooth type | Dog | Cat |
---|---|---|
Deciduous dentition | ||
Incisors | 3–4 weeks | Entire dentition starts to erupt at 2 weeks and is complete by 4 weeks |
Canines | 5 weeks | |
Premolars | 4–8 weeks | |
Molars | Absent | |
Permanent dentition | ||
Incisors | 3.5–4 months | 12 weeks |
Canines | 5–6 months | |
Premolars | 1st premolars 4–5 months; remainder 5–7 months | Variable; full dentition present by 6 months |
Molars | 5–7 months |
Salivary glands
The positions of the glands are:
< div class='tao-gold-member'>