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THEORIES ABOUT ORIGIN OF CHORDATES It is believed that Chordates have originated from invertebrates. It is difficult to determine from which invertebrate group the chordates were developed. Chordate ancestors were soft bodied animals. Hence they were not preserved as Fossils. Many biology theories were put forward to explain…
In Eutherian mammals the embryo develops in the uterus of mother. The developing embryo will get nourishment from mother through the placenta. Placenta is not common to all mammals. It is developed well in Eutheria The term placenta was delved from Greek word it means flat cake. Placenta is a…
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…
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…
Two main theories have been proposed to explain the evolution of molars. 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…
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…
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…
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 -…
SKIN STRUCTURE AND FUNCTIONS IN MAMMALS The body of Rabbit is covered by skin. It shows two layers, Epidermis 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…
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,…
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…
THERIA This group includes Mammals which show true mammals characters Infraclass Metatheria: They show almost all the Mammalian characters. Females show brood pouch or Marsupium on their ventral abdomen. Sebaceous glands are modified into mammary glands. Pelvic girdle shows epipubic bones. This supports Marsupium. Ribs are two…
Mammalia is divided into two subclasses. 1) Prototheria 2) Theria GENERAL CHARECTERS OF PROTHERIA External pinnae are absent. In the young stage teeth are present and in the adults horny plates are formed. Mammary glands are present and tears are absent. Body is covered by hairs. Pelvic girdle…
Mammal like Reptiles therapsida might have given Mammals. It occured at the end of Triassic period of Mesozoic era. In Jurassic period only few mammals existed. In the coenozoic era these animals increased their number and became very complex. This era is called 'age of mammals'. Today nearly 8500 species…
In the eye of the bird a comb like structure is present. It is called pecten. It is soft and vascular. It is a rectangular plate. It projects into the vitreous humour from the blind spot. Functions of Pecten: It protects the retina from sunlight by casting shadow…
In the birds vertebral column compound structure is present. It is called Synsacrum. It is formed by the fusion of 14 to 16 vertebrae. Those vertebrae are one last thorasic vertebra, Six lumbar vertebrae, two sacral vertebrae and seven candal vertebrae. This structure supports llia of the pelvic girdle. The…
