Class : Mammalia - Reptilia - sub phylum : Tetrapoda

 Tetrapoda

 

The vertebrates with two pairs of limbs adapted for locomotion on land are known as tetrapods. The limbs are of pentadactyl type. The tetra-pods are identified by a cornified outer layer of skin and nasal passages communicating with mouth cavity and lungs. The super class Tetrapoda is divided into four classes namely. Amphibia, Reptilia, Aves and Mammalia.

 

 

Amniota

 

The tetrapods like reptiles, birds and mammals are referred to as amniotes. The amniotes have certain membranes associated with embryos inside the egg. It is an adaptation in terrestrial forms during development. These membranes are the amnion, chorion and allantois.

 

Class : Mammalia

 

The term 'mammalia' was given by Linnaeus (1758) to that group of animals which are nourished by milk from the breasts of the mother. They are a successful group, for they adapt themselves readily to new situations and to new food habits.

The body is generally covered with epidermal hairs. The integument is provided with sweat, sebaceous and scent glands. The mammary glandsare modified integumentary glands. The external ear or the pinna is present in most of the mammals. A muscular diaphragm is present in between thoracic and abdominal cavities. It helps in respiration. The red blood corpuscles are non-nucleated, biconcave and usually circular in form. The heart is four cham-bered. Only the left aortic arch is present. In brain cerebral hemispheres are very large and highly convoluted.

 

Corpus callosum, a transverse band of nerve fibres connecting the two ce-rebral hemispheres, is present. Dentition is thecodont, heterodont and di-phyodont. Cloaca is absent. Testes lie outside the body cavity, enclosed in scrotal sacs. Eggs are small with little or no yolk. Fertilization is always inter-nal. Mammals are Viviparous ie., they give birth to alive young ones. Pla-centa is usually present.

The class Mammalia is subdivided into three subclasses namely

Monotremata, Marsupialia and Placentalia.


Comments

Post a Comment

Popular posts from this blog

Plasma Membrane

  Plasma Membrane   It is the outer limiting membrane of both prokaryotic and eukaryotic cells. It is an ultra thin, elastic, living membrane. Plasma membrane is a dy-namic and selective transport barrier.   Since the plasma membrane is ultra thin, it could be observed only under electron microscope. Structure of the membrane is studied by isolating the same from the cell and conducting biochemical investigations.   In 1895  Overton  suggested that the membrane is made of fatty sub-stances. Other workers later concluded that two layers of lipid were present in the cell membrane. According to a model proposed by  Danielli  and  Davson  in 1935, the  lipid bilayer  of the membrane was coated on either side with protein.   In 1960,  Robertson  using electronmicrographs proposed a  unit   membrane hypothesis . According to this hypothesis the two outer layers of  protein are about 2 nm thick and appear densely granular. They enclose a   clear central area of about 3.5 nm wide consisting of
Read more

THEORIES OF EVOLUTION : Neo-lamarckism

  THEORIES OF EVOLUTION   Neo-lamarckism   Lamarck's 'theory of inhertitance' was further studied by a group of scientists. Their ideas supporting Lamarck's opinion collectively constitute neo-Lamarckism.   The neo-Lamarckians were of the opinion that 'adaptions' are universal in nature. An adaptation happens through causal relationship of structure, function and environment. Due to changes in the environment, habits and life style of organism gets altered. Thus gradually the organism acquires new structures. The newly obtained character gradually becomes an inheritable trait. This opinion and argument is a modified form of Lamarckism. These ideas stressed direct action of environment on organisms.   Support to neo-Lamarckian concept - Experiments   1. McDougall (1938) tried to prove that learning is an acquired character that can be inherited. He did his experiments on rats.   He deviced a 'T' shaped tank. The tank had two exits. One exit was well light
Read more

History of Human anatomy

  History of Human anatomy   The term 'anatomy' is Greek in origin. It takes its root from 'ana' and 'tome' (ana-up ; tome-cutting). Thus anatomy is the science of physical structure of an animal or plant studied by dissection. The Human Anatomy provided the necessary knowledge for surgery and medicine.   The study of human anatomy dates back to 2500 BC, when the Egyptians prepared mummies. They removed internal organs of cadavers be-ing mummified. They also did surgery for wounds and broken bones. In India during 500 - 491 BC Susruta performed cataract operation. In 1 st  century AD, Celsus, a Roman physician wrote about surgical procedures.   The year 1543 AD was significant due to publication of an accurate book on Anatomy by Andreas Vesalius. In 1628 William Harvey described the functioning of heart and the movement of blood in animals. These earlier works were followed by the discovery and accurate account of each and every or-gan system and organs in human
Read more