244 Observations on the progressive Aiotion of Snakes. 



may be considered as hoofs or shoes, are the best fitted for 

 this kind of progressive motion ; there is, however, a si- 

 milar structure of ribs and muscles in the anguis and am- 

 phisbaena. 



In the anguis the ribs are proportionally weaker; and as 

 these have nothing to correspond with the scuta, it is pro- 

 bable this mode of progressive motion is less necessary to 

 them. 



The rings of the amphisbaena are a near approach to the 

 large scuta. 



Description of the Plates. 

 Plate VI. 

 A lateral view of the muscles of the boa constrictor. 

 AA. The straight muscles of the back. 

 BB. The first set of muscles which arises from the trans- 

 verse process of each veriebra, and is inserted into the rib 

 behind it close to its head. - • 



CC. The second set. 

 BD. The third set. 

 EE. The fourth set. 

 FF. The fifth set. 



GG. Short muscles which pass from cartilage to cartilage. 

 HH. A set of oblique muscles which passes from the 

 anterior side of the bony extremity of each rib to the pos- 

 terior edge of each scutum. 



II. Muscles which pass from the ribs near their heads 

 obliquely backwards, to be inserted into the skin at the edge 

 of each scutum. 



K. Muscles of the scuta. 



Plate VII. Fig. 1. 

 An internal view of the abdominal muscles of the boa 

 constrictor. 



AA. The inuscles which pass from cartilage to cartilage 

 of the different ribs. 



BB. A set of muscles which passes from the point of 

 each rib over two ribs to the middle of the third. 



CC. A similar set of muscles continued from the op- 

 posite side of the rib, passing over three ribs to the body of 

 the vertebra. 



DD. The abdominal muscles which arise from the an- 

 terior edge of each rib, and pass to the linea alba. 

 EE. The linea alba. 



FF. The termitialion of the set of oblique muscles which 

 passes from the bony extremities of the ribs to the edges of 

 the scuta. 



GG. The 



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