- Monocuspici teeth - Teeth with one cusp or tubercie
- Bicuspid teeth - Teeth with two cusps.
- Tricuspid teeth - Teeth with three cusps and all the cusps are arranged in one plane by forming a triangle.
- Bunodont teeth - Teeth with a number of distinct blunt pointed cusps - Man and Monkey.
- Lophodont teeth - The cusps are fused in the form of ridges- Horse & Elephant.
- Selenodont teeth - Here the cusps are wear away, exposing the under lying dentineythich-getnuii by crescent -Shaped bands raf -
- Secodont teeth - The cusps are having sharp cuffing surfaces - carnivorous mammals. Carnassial teeth are present.
- Hypsodont teeth - The teeth are having long crown and deeply placed neck. - Horse
- Brachyodont teeth - Teeth with short crow, and neck at the surface gum. - Dog.
In the beginning the buccal epithelitim of the gum sinks down forming the t ridge. Simultaneously, the cells of malpighian layer of epidermis grow and move into the epidermis forming the dental lamina. Along the dental Lamina, the mesenchymal cells multiply and condense into a dental papilla or tooth bud. This grows upwards and pushes the dental kA Thereby an inverted cup form assumed The malpighian cells become markedly columnar and are known as ameloblasts. The mesenchymal ce are differentiated into a layer of odontoblast cells.
The tooth bud is now as ‘enamel organ’. The ameloblast cells secrete enamel’ towards their inner side, while the odontobiasts secrete ‘dentine’. The enamel sur rounds the upper part of dentine like a cap. The remaining mesenchyme cells of the dental papilla form the ‘pulp’ and the cavity of the enamel organ modifies into the pulp cavity. Sooner, the development of the tooth is completed,. The jaw bone forms a socket or alveolus around its base. The tooth increases in size by the secretion of more or mote dentine and finally emerges out from the gum. The odontoblasts now secrete cement around the neck and root of the tooth narrowing the pulp cavity. In majority of the mammals, the odontoblasts stop functioning after the development of tooth and the tooth stops growth. In some cases, like incisors; of rodents and tusks of elephants, the odontobiasts are functional throughout the life and the teeth continue to grow.
- CONCRESCENCE THEORY OF ROSE
- TRLTUBERCULAR THEORY OF COPE & OSBORN
According to the concrescence theory, the molar tooth has evolved by the fusion of several simple cone-like teeth. This theory Is now abandoned in favor of the second with is now accepted with certain modifications.
Cope & Osborn theory is based on the paleontological evidence. As such the mammalian molar has been derived from a simple reptilian cone by the development of additional cusps. The Mesozoic mammal, the crown of the molar tooth has three cusps arranged more or less in the form of a triangle. This pattern of tooth has been termed tritubercular. It is assumed that the molars of the modem mammals have originated from the primitive tooth by the development of lateral cusps.
In the upper molars the three cusps are known as paracone, protocone, and metacone, The protocone lies on the apex at the inner side, the paracone lies external to it and the metacone to the back of the paracone. In the lower molars the cusps are named protoconid, paraconid and metaconid. The protoconid and metaconid are anterior and posterior to it in position. These cusps are joined by the ridges and later bell-like extensions or talons are produced from the ridges and additional cusps form on them. In this way, the various types of mammalian molars have evolved.
- Root: It is the basal part embedded in the bony socket.
- Neck: it is the part above the root enclosed by the gum
- Crown It is the upper part beyond the surface of the gum.
- Pulp cavity: The entire tooth encloses a central pulp cavity surrounded by a layer of odontoblast cells filled with soft pulp. It is made up of connective tissue, blood vessels and nerve fibers.
- Dentin: A substance chemically similar to bone- dentine forms the major part of the tooth. But the dentine is permeated by numerous thin canaliculi.
- Enamel: It is present over the de in the crown and neck regions of the tooth. It is hardest and contains only traces of living matter.
- Cement: It surrounds the denting of the root portion of the tooth. It is bony in nature.
What are the symptoms of heat rash?
- Heat rash does not go away on its own within a few days.
- You develop an infection in an area where you recently had heat rash.
How can I prevent heat rash?
The body of Rabbit is covered by skin. It shows two layers,
1. Epidermis: It is the upper part of the skin. It is divisible into two parts
a) Stratum comeum: This layer is hard scale like, dead keratinized and flat.
Keratin prevents the passage of water and solutes. This layer is cast off periodically. Below this layer transparent layer is present It is called stratum lucidum. In this layer - iucidin substance is seen When stratum comeum is removed this lucidum layer will become stratum comeum Below the stratum lucidum another layer is present. It is called stratum granulosum. It contains granular cells. Final layer of epidermis is stratum germinatum. It shows columnar cells. These cells can undergo division.
In the epidermis special pigment cells are present they are called chromatophore cells.
2. Dermis: It is present below the epidermis It is tough and flexible. It is made by connective tissue, unstrapped muscles blood capillaries, nerves and fat cells This part of the skin is in contact with nerve endings.
The sebaceous glands are sac like glands. They are branched. They secrete oily secretion which keeps the hair and skin water proof.
The sweat glands are thin and long tubes. They arc coiled the sweat glands are found deep in the dermis. They open on the surface of the skin. These glands will secrete salty, watery solution from blood. It is excretory in function. This gland plays an important role in the regulation of body temperature.
Hair: It is epidermal in origin. It is seen only in mammals. It develops from the stratum germinatum. It has two parts root and shaft the hair is enclosed in a tube like hair follicle. At the base of the follicle dermal papilla is present. It is supplied with blood vessels.
The skin covers the body and protects the body organs
- It covers the body parts.
- Sweat glands are excretory and regulate the body temperature.
- Skin works as tactile sense organ.
- Sebaceous glands are modified into mammary glands which secrete milk for young ones.
The ribs articulated with sternum by their cartilage part. In rabbit the first pair of ribs are attached to the presternum.
Uses of sternum :Thus sternum gives strength and support to the body on the ventral side. It helps in the process of respiration also.
- Scala vestibuli
- Scala tympani.
The middle cavity is filled with endo lymph membranes that cover the Cochlea are Reisner's membrane and membrane. The epithelium of basilar membrane is highly modified. It is "organ of corti". It has hair cells and supporting cells. It is supported by cochlear branch of 8th cranial nerve. It is useful for hearing.