Teeth Modifications in Mammals

Written by Monday, 03 July 2017 15:37
There is an interrelation between the form of teeth arid nature of food. These may be omnivorous, carnivorous, insectivorous herbivorous and rodents or gnawing. In Mammals dentition is complete in the first three types. Often incomplete in herbivores where the canines are absent. The absence of canines forms a gap between incisors and premolar. This is called diastema Rabbit). The canines are small or absent and the cheek teeth have broad grinding surfaces with transverse ridges - lophodont molars. In omnivorous mammals the incisors are suited for cutting the canines for tearing and cheek teeth with prominent crowns raised into rounded tubercles are adapted for crushing bunodont molars. In the carnivorous mammals, the incisors are either poorly developed or reduced and few in number and the canines are long and sharp suited for tearing and piercing the flesh But the molars with knife-like edges are modified for scratching the flesh from the bones. In the insectivores, the incisors of the upper and lower jaws become closely united to secure small active prey and the molars have sharp pointed crowns.
Depending upon the shape, size and number of cusps, the teeth are differentiated into:
  1. Monocuspici teeth - Teeth with one cusp or tubercie
  2. Bicuspid teeth - Teeth with two cusps.
  3. Tricuspid teeth - Teeth with three cusps and all the cusps are arranged in one plane by forming a triangle.
  4. Bunodont teeth - Teeth with a number of distinct blunt pointed cusps - Man and Monkey.
  5. Lophodont teeth - The cusps are fused in the form of ridges- Horse & Elephant.
  6. Selenodont teeth - Here the cusps are wear away, exposing the under lying dentineythich-getnuii by crescent -Shaped bands raf -
  7. Secodont teeth - The cusps are having sharp cuffing surfaces - carnivorous mammals. Carnassial teeth are present.
  8. Hypsodont teeth - The teeth are having long crown and deeply placed neck. - Horse
  9. Brachyodont teeth - Teeth with short crow, and neck at the surface gum. - Dog.
In sirenia (sea - Cow and Manatee), the teeth are devoid of enamel.


Written by Sunday, 02 July 2017 21:54
The tooth develops partly from the epidermis and partly from the mesenchyme of dermis. Its enamel is derived from the epidermis and the remaining parts from the mesenchyme. Mammalian teeth develop in two sets. The milk or deciduous teeth develops from the buccal epithelium of the gums which are replaced later by the permanent teeth.The tooth develops partly from the epidermis and partly from the mesenchyme of dermis. Its enamel is derived from the epidermis and the remaining parts from the mesenchyme. Mammalian teeth develop in two sets. The milk or deciduous teeth develops from the buccal epithelium of the gums which are replaced later by the permanent teeth.

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.
tooth development 2 thumb36

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.
tooth development mammales thumb14


Written by Sunday, 02 July 2017 18:55
Two main theories have been proposed to explain the evolution of molars.

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.


Written by Sunday, 02 July 2017 18:10
Teeth are the dermal derivatives of integument They are developed as a result of calcification in the mucous membrane of the 1 cavity. Along with the ridge of the two jaws, the teeth are arranged in a row. The teeth are present in almost all the mammals except in a few mammals In whale, the teeth are fused into plates and lost in the adult stage of Ant eaters. But in Echidna (spiny ant eater) the teeth are absent even in the embryo.
Structure of tooth: Each typical mammalian tooth is placed in the socket over the jaw bone. It is distinguished into three main pads.
  1. Root: It is the basal part embedded in the bony socket.
  2. Neck: it is the part above the root enclosed by the gum
  3. Crown It is the upper part beyond the surface of the gum.
The toot is separated from the socket by a vascular pridontal membrane. The vertical section tooth consists of the following parts.
  1. 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.
  2. Dentin: A substance chemically similar to bone- dentine forms the major part of the tooth. But the dentine is permeated by numerous thin canaliculi.
  3. 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.
  4. Cement: It surrounds the denting of the root portion of the tooth. It is bony in nature.


Written by Sunday, 02 July 2017 17:05
The mammalian teeth are placed in the muscular sockets in the jaw bones. This type of dentition is called Thecodont. The teeth are ‘diphyodont’. Two sets of teeth develop during life lime. The first set of teeth develop in the young and known as ‘milk or deciduous teeth’, after certain age these are replaced by the second set of permanent teeth. But in bats ‘and, guinea pigs the milk teeth are shed before birth. In platypus, toothed whales, sloths and sirenians the monophyodont dentition’ is present. Milk dentition is reduced by the replacement of the third premolar in marsupials.
All the teeth are not alike in all mammals. Mostly mammals exhibit ‘heterodont dention’. The teeth are modified in the form and function. But in Dolphins and porpoises it is homodont (all teeth are alike). There are four types of mammalian teeth.
1) Incisors: These are present on the premaxillae bones of the upper jaw and dentary bones of the lower jaw. They have only one ro and sharp cutting edges. So this type of teeth is used in sizing and cuffing.
2) Canine: These are present between the incisors and premolar. There is a single such troth in each half of each Jaw. These are long, conical teeth with a single root and simple, sharp-pointed crown.
3) Premolars : These follow the canines. They have double root and compressed crown with one or two cusps. These possess grinding and crushing surfaces. Premolars are replaced once in life time.
4) Molars: These are next to the premolars. They have more than two roots and cusps. These do not have predessors and always develop in the permanent set. Molars are used for crushing and mastica lion.
Both prermolars and molars are collectively knows, as cheek teeth and are borne on maxillae and dentaries. These have broad crushing and grinding surfaces or cusps.


Written by Sunday, 02 July 2017 16:37
Mostly the number of teeth is fixed in each mammalian species. Mammalian heterodont dentition is expressed by a ‘dental formula’. The number and arrangement of teeth in each half of the upper and lower jaws is constant and identical. Hence the teeth can be expressed by using the initials - I, C, Pm and P4. The number of teeth differs in the various orders of mammals and is closely related to their ‘feeding habits. Typical number of teeth in the mammals is 44. This can be observed in Horse and pig and their dental formula is
 dental formula thumb10
The numerator indicates the number of teeth on one side of upper jaw. The denominator indicates the number of teeth on one side of the lower jaw. As the two halves of each jaw have same number and kind of teeth, the number of teeth on one side alone is usually ex pressed in the formula.
The dental formulae of some common mammals are given below
dental formula man pig horse cow thumb17

Prickly Heat Rash: Cause, Symptoms and Treatment

Written by Sunday, 02 July 2017 15:39
Prickly heat usually clears up on its own within a few days. However, in serious cases heat rash can interfere with the body's heat-regulating mechanism and cause heat exhaustion.
Heatstroke is a more serious condition when the body can no longer cool itself. This is a medical emergency.
What causes prickly heat rash?
Heat rash begins with excessive perspiration, usually in a hot, humid environment. The perspiration makes it easier for dead skin cells and bacteria on the skin to block the sweat glands, forming a barrier and trapping sweat beneath the skin, where it builds up, causing the characteristic bumps. As the bumps burst and sweat is released, there may be a prickly, or stinging sensation that gives this condition its name.

What are the symptoms of heat rash?
Small, itchy red bumps on the skin are the symptoms of heat rash. The rash may feel prickly, stinging or burning.
Seek medical advice if:
  • 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.
What are the treatments for heat rash?
In most cases, heat rash will clear up on its own in a few days if the affected area is kept cool and dry. Avoid excessive heat and humidity and cool off with a fan, take a cool shower or bath and let your skin air dry, or if you have air-conditioning, use this to cool yourself. Once the skin is cool and dry again, don’t use any type of oil-based product, which might block your sweat glands. Calamine lotion and/or hydrocortisone cream can relieve itching and irritation.
If your prickly heat does not go away within a few days, or if you develop an infection where the bumps have burst, you may need medication, so seek medical advice.

How can I prevent heat rash?
To prevent heat rash, avoid situations that can lead to excessive sweating, such as hot, humid environments and strenuous physical activity. In hot weather, use fans and cool showers and baths to stay cool, or air conditioning if available; dry your skin thoroughly; and wear lightweight, loose-fitting clothes ideally made from cotton.


Written by Sunday, 02 July 2017 15:39

The body of Rabbit is covered by skin. It shows two layers,
  1. Epidermis
  2. Dermis
Associated with skin are hair, claw and glands.

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.
Glands: In the skin of Rabbit sweat or sudorif glands and sebaceous glands are present.

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
Skin Functions:
  1. It covers the body parts.
  2. Sweat glands are excretory and regulate the body temperature.
  3. Skin works as tactile sense organ.
  4. Sebaceous glands are modified into mammary glands which secrete milk for young ones.


Written by Sunday, 02 July 2017 15:31
In the mid ventral region of thorax of Rabbit sternum is present. It is made by five bony pieces called "Sternabrae". It is called "mesosternum". This will show "presternum" anteriorly. It is a long bony piece. It is connect­ed with clavicles. On the lower side mesosternum it articulates with xiphi-sternum, which ends with xiphoid cartilage.

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.


Written by Sunday, 02 July 2017 08:08
The internal ear of rabbit includes "organ of corti" or Cochlea spirally coiled. Lagena is enclosed and fused with the spirally coiled j the preotic bone which form cochlea. Cochlea is a bony tube line connective tissue. The cavity of the cochlea is transverse by two brines. It is divided into 3 cavities. They are
  1. Scala vestibuli
  2. Media
  3. 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.
  1. Posterior semi circular canal
  2. External semi circular canal
  3. Anterior semi circular canal
  4. Ampullae
  5. Utriculus
  6. Sacculus
  7. Ligament.
  8. Cochlear duct

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