322 



AMPHIBIA 



by the rectus abdominis is supported laterally by thin sheets of 

 muscle-fibres running up to the vertebral column, the obliquus exter- 

 nus and transversus abdominis (Fig. 191). 



In the anterior region the hypaxial muscles have become restricted 

 to the throat, where they form the hyoid musculature, which by raising 



Fig. 192. a. Lateral surface of the fin of Neoceratodus, showing the abductor 



muscle-bundles, b. Section through the fin in the transverse plane, showing the 



arrangement of the muscle-bundles as abductors and adductors. 



ab. abductor muscles; ad, adductor muscles; g. pectoral girdle; h. horny fin rays; 



r. radials. (From Ihle, after Braus.) 



and lowering the floor of the mouth is the main agent of breathing. 

 The submaxillary muscle runs transversely between the rami of 

 the jaw. Deep to this lie other muscles, including the sternohyoid, 

 close to the midline, which is a forward continuation of the rectus 

 abdominis. 



12. The limb muscles of Amphibia 



The muscles of the limbs were presumably derived from the radial 

 muscles that moved the fins of fishes. These are formed from the 

 myotomes and they are mainly arranged so as to raise and lower the 

 fin (Fig. 192). In modern amphibia the limb musculature is still partly 

 formed from myotomes (Griffiths, 1959). The segmental origin of the 



