OSSEOUS SYSTEM. 143 



this part of the sternal apparatus in the Lizards. In Trionyx and 

 Chelonia, the apices of the ribs are free, and abut against marginal 

 scutes, which never become anchylosed to them. In Testudo and 

 Emys the dorsal scutes are most perfectly developed, but they are all 

 blended together, and united by suture. 



The typical structure of the Scapula and Clavicle is best exem- 

 plified in the Tailless Batrachia, or the Frogs, whence we will 

 pass to consider its modifications in the other orders. The Scapula 

 consists in the. Frogs of two bony plates, the superior one of which 

 rests upon the transverse processes of the anterior vertebra, the 

 inferior narrower helps to form, along with the two succeeding 

 bones, the articulating surface for the humerus. The clavicles are 

 two in number upon either side ; the anterior one is narrow, and 

 flattened like a scale, the posterior is broader ; they both diverge 

 from each other in front, and come in contact in the middle line 

 with their fellows of the opposite side, so that the anterior coalesces 

 with the anterior, the posterior with the corresponding piece of the 

 sternum. 



Next in order to the above, we have to consider the structure of 

 these parts in the Chelonia. The Scapula is in them a longer and 

 narrower bone, slightly and loosely connected superiorly by liga- 

 mentous bands with the first cervical vertebra, while inferiorly it 

 is continuous directly with the anterior and also narrow clavicle, 

 so that the two bones are anchylosed into a single one. The poste- 

 rior clavicle is mostly broader, and expanded in the form of a shovel 

 at its free extremity, which is directed backward, while in front it 

 unites with the two former bones by means of synchondrosis, to form 

 the articulating cavity for the humerus. The whole of this osseous 

 girdle is completely covered by the carapace and plastron, and is 

 therefore not visible externally. 



In most of the Sauria, the scapula, as in the Frogs, is formed of 

 two pieces. The posterior clavicle is very broad, projects into seve- 

 ral points, which abut against a cartilaginous piece that is united to 

 the sternum, and a corresponding cartilaginous piece of the other side. 

 The anterior clavicle is rib-shaped, and does riot contribute in any 

 way to the formation of the shoulder joint. Both the anterior clav- 

 icles abut against each other in the middle line, and together form 

 a narrow arch in front of the T-shaped portion of the sternum. 

 The above arrangement of parts is principally displayed by the 

 Lacertae, and other closely-allied genera. The Crocodiles have a 

 single elongated scapula, and also a single, tolerably broad and flat 



