General Considerations on Animal Form (Vertebrates), Study notes of Animal Anatomy and Physiology

Download General Considerations on Animal Form (Vertebrates) and more Study notes Animal Anatomy and Physiology in PDF only on Docsity! General Considerations on Animal Form (Vertebrates) Descriptive Terms Body of vertebrate is carried in the horizontal position, and the surface are designated as follows with the reference to this position: ● Dorsal —back or upper side (Posterior in human anatomy) ● Ventral —under side (Anterior in human anatomy) ● Lateral —sides, right and left ● Median —middle ● Anterior/ Cephalic/ Cranial —head end of the animal (Superior in human anatomy) ● Posterior/ Caudal —tail end of the animal (Inferior in human anatomy) Adverbs made by substituting “d” for the end letter of these words mean “in the direction of,” Example: (Cranial) Craniad - towards the head (Caudal) Caudad - towards the tail Other Descriptive Terms ● Central —part of a system nearest the middle of the animal ● Peripheral —part nearest the surface ● Proximal —near the center ● Distal —away from the center ● Superficial —on or near the surface ● Deep —some distance below the surface ● Superior —above ● Inferior —below Ventral Lateral (Right) Median Posterior Anterior dinal or posterior axis Horizontal or Frontal Plane Transverse or Mediolateral Axis any line in the transverse plane running from sige to side Transverse Plane Symmetry The forms of symmetrical animals are dependent upon the arrangement of their parts with regard to the foregoing axes and planes. There are four fundamental types of animal symmetry: 1. Spherical symmetry 2. Radial symmetry 3. Bi-radial symmetry 4. Bilateral symmetry Since the study will be about vertebrates and all vertebrates are bilaterally symmetrical, other types of symmetry will not be considered in this note. Bilateral symmetry —parts of a bilaterally symmetrical animal are arranged symmetrically with reference to three axes: 1. longitudinal 2. transverse 3. sagittal axes; two ends of the sagittal axis in any given cross-section are unlike There is only one plane of symmetry in such an animal—the median sagittal plane. The median sagittal plane divides the animal into approximately identical right and left halves, which are mirror images of each other. If the structure of vertebrates are cut in half by the median sagittal plane, in which case it is then called as unpaired structures. If the structure of vertebrates are placed symmetrically on each side of this plane at equal distance, they are called paired structures The digestive tract is the only system which does not show a symmetrical relation to the median plane in the adult. However, it is bilaterally symmetrical in early embryonic stages. Metamerism (Segmentation) Metamerism (also called segmentation) is the regular repetition of body parts along the anteroposterior axis (longitudinal axis). The body of segmented animals is composed of a longitudinal series of divisions in each of which all or most of the body system are represented by either the entire paired organs/parts or by a portion of the median unpaired structures. Each division of the body is termed a segment, metamere or somite —This exhibits both external and internal segmentation. For example: Earthworms are divided into similar segments, by distinct ring-like grooves, called segments, somites, or metameres. If the anterior and posterior boundaries of each segment may or may not be marked externally by a constriction of the body wall then it exhibits internal metamerism only. An ideal segmented animal would consist of a series of identical segments; but no animal like that exists, since the head and terminal segments are necessarily different from other segments. However, primitive ringed worms like the Nereis, are close to the ideal segmented animal. The segmentation of the animal body into nearly identical segments is known as homonomous segmentation. Homonomous segmentation is a primitive and generalized state in which the various segments are more or less independent and capable of performing all necessary functions. In the evolution of segmented animals there has been a continuous development from the homonomous to the highest degree heteronomous condition.