Sauropsida: Class Fleptilia 



47:5 



Conn series from head to end of tail (Fig. 88). The paired fins are 

 relatively small and capable of only a few simple motions for which no 

 elaborate set of muscles is required (Fig. 93). The most complex set 

 of muscles in the fish is the branchiomeric system, which effects the 

 respiratory movements in the gill-region. The pentadactyl leg, with 

 its basal girdle, three jointed segments, and five digits, at once requires 

 a set of muscles much more complex than that of a one-segment lateral 

 fin. The high degree of mobility of the reptilian head and neck depends 

 upon a corresponding degree of differentiation of muscles in those 

 regions. In the anterior or "'thoracic" region of the trunk, there must 

 be mnseles specialized to effect the respiratory movements (Fig. 

 366, bottom). The muscles of the abdominal part of the body-wall show 

 least specializing of the primitive myomeres. Altogether, therefore, the 

 muscular system of reptiles is vastly more complex than that of fishes, 

 and considerably more so than that of amphibians (Fig. 366, top). 



The kidney of an adult reptile differs from that of an amphibian. 

 At a very early stage in the development of a fish or amphibian, a small 

 number of excretory (renal) tubules develop at the anterior end of the 

 coelom. The several tubules of each side constitute, in effect, an em- 

 bryonic kidney, the pronephros. These structures, however, are 

 briefly transitory and are replaced by a more extensive set of paired 

 tubules which develop in a more posterior position. Those on each side 

 become elaborated and compacted into a definite organ, the meso- 



DIGAST01CU5 



Fig. 366. Superficial lateral trunk muscles in an amphibian and a reptile. (Top) 

 Neclurus. {Bottom) Sphe.nodon. (Courtesy. Neal and Rand: "Chordate Anatomy," 

 Philadelphia. The Blakiston Company.) 



