VIF.] 



THE COMMON FROG. 



97 



tail, which is the usual mode of swimming among 

 vertebrate animals — that made use of by sharks and 

 porpoises, as well as by the overwhelming majority of 

 fishes. 



Studying the life-history of this one animal, then, 

 we become acquainted with a process of direct tran- 



FiG. 60. — Anterior muscles of the Trunk of Man : the pectorah's major of the rij^ht 

 side ai.d the left external oblique being removed, i, pectoraiis major : 2, pec- 

 toralis minor ; 3, subclavius ; 4, serratus magnus ; 5, internal intercostals ; 6, 

 external oblique ; 7, internal oblique ; 8, linea alba. 



sition from the condition of a fish to that of a quad- 

 ruped, as regards a most important group of organs. 



In ourselves, the back is provided with muscles 

 which extend along its length in a complex series of 

 longitudinal divisions, from the middle line outwards. 



The abdomen of man is inclosed and protected by 

 successive m.uscular layers laid one upon another, the 



H 



