i\[USCLES 133 



back-bone ; but they, at least, take tlie place of riljs, 

 and in this sea-tiirtle noted their freedom hints that 

 they really are such. So likewise tortoise-forms have 

 no breast-bone, but their lower shell takes its place, 

 though the bones of this shell have their orig^in in the 

 skin. There are many peculiarities in the ribs of 

 reptiles which we can not even mention. 



Those of the serpents and flying lizards have been 

 noted under Miction. In crocodilians the breast-bone 

 runs back to the thigh- junction, and peculiar ribs, 

 loose at their upper ends, are attached to it ; and in 

 the Tuatera there are ribs in the abdomen not found 

 connected with anything else. Perhaps the slightest 

 hint of the lower shell of the tortoises may lie in this. 



The Skull of the reptile is more complete than 

 in the amphibians — that is, the box is more perfect 

 — better roofed-in. In all cases but one (which is not 

 normal) it joins the first vertebrge of the back-bone by 

 only one ball-and-socket joint — the ball being on the 

 skull. The skull is much like that of birds and some 

 very low mammals — as the opossums ; but from these 

 last, it is sufficiently distinct, if we could specify with- 

 out being tedious and technical. The lower jaw's con- 

 nections to the skull have been noticed. 



Muscles 



Muscles of reptiles are especially interesting to 

 students because of wdiat they hint of the origin of 

 pecuhar muscles in birds and mammals ; but the sub- 

 ject is too broad to discuss here. They all tend to be 

 redder than those of the amphibians — having a better 



