22 

 The Vertebrate Body 



Support, Protection, Movement, and Coordination 

 in the Frog and Man 



As we have studied the animal kingdom, we have chosen a type ani- 

 mal from each phylum to illustrate the characteristics of that phylum. 

 This has not been a difficult task, since in every phylum there has been 

 one that was somewhat representative of the entire group. The task is 

 much harder for the chordates, however, because of the great diversity 

 of animals that are included. By popular accord of competent zoolo- 

 gists the frog seems to be the animal chosen for this purpose. It lies 

 between the lowest and the highest of the group, it is both a land and 

 water animal, and it is common and easily obtained for laboratory study. 

 Therefore, we will survey the systems of the frog as a representative of 

 this important phylum of animals. However, since man is also in this 

 phylum and we are particularly interested in this species of animal, we 

 will include discussions of the human body along with the study of the 

 frog. Superficially, the frog would not appear to have much in common 

 with man, but the general plan of body organization is the same and 

 much that is said about the frog will also apply to man. Therefore, it 

 will be rather easy to gain some insight into the life processes of the 

 human body by comparison with those found in the frog. The impor- 

 tant differences between the two will be pointed out at the end of the 

 discussion of each of the systems. 



The Skeletal System. The general functions of the skeletal system 

 are support, protection, and muscle attachment. The skeleton of the 

 frog is composed largely of bone and does a very good job of supporting 

 the softer parts of the body. There is a case of bone around the brain 

 and spinal cord, so these vital organs are protected, but there is very 

 little protection of the rest of the body. The large voluntary muscles of 

 the body need some solid attachment in order to function, and the bones 

 serve this purpose. 



Since the bones are not very flexible there must be numerous movable 

 joints between them to allow for body movements. However, body 

 movements would be very noisy and there would be a lot of friction if 

 the edges of the raw bone ground against one another at the joints. This 



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