REPTJLIA. 547 



cavity, and united by a double articulation both with the trans- 

 verse processes and the bodies of the vertebra. The head of the 

 last rib of the Crocodile is, in fact, simple, and merely articulated 

 with the apex of the transverse process of the corresponding verte- 

 brae ; the next is slightly bifid at its origin, but both the divisions 

 are still connected with the transverse process : as we advance still 

 further forwards, the division of the origin of the rib becomes more 

 and more decided, until at length, at about the fifth rib, we have two 

 distinct heads, one firmly articulated with the body of the vertebra, 

 the other with the transverse process ; presenting an arrangement pre- 

 cisely similar to that met with in the structure of the thorax of a bird. 

 (598.) The sternal apparatus is not less interesting to the osteo- 

 logist. The anterior extremity of the sternum is osseous, and 

 considerably prolonged forwards, to be articulated with the clavi- 

 cles, and thus afford a support to the anterior extremity. Behind 

 this it becomes cartilaginous, and affords attachment to the sternal 

 ribs, which enter into the composition of the thorax : it does not, 

 however, terminate at the posterior margin of the thoracic cavity, 

 but is continued along the mesial line of the abdomen quite to the 

 pubis, and gives off eight abdominal sternal ribs, to which no 

 dorsal correspondents are met with. These abdominal ribs serve 

 to support the muscles of the abdomen, and here present their 

 maximum of developement : rudiments of them are, however, still 

 met with in the higher animals, and even in the human subject 

 we find, in the transverse tendinous bands which intersect the 

 substance of the rectus muscle of the abdomen, the last remains 

 of these appendages to the sternal portion of the skeleton. 



(599.) In the anterior extremity of the Crocodile we have most 

 of the parts enumerated as entering into the composition of a per- 

 fect or typical skeleton ; the shoulder, however, is composed of only 

 two pieces, the Scapula and the Clavicle, the last of which articu- 

 lates with the sternum : the bones of the arm, fore-arm, and hand, 

 are completely developed. 



(600.) The posterior extremities are fully formed, the pelvis 

 being connected by means of the ossa ilii to the transverse pro- 

 cesses of two vertebrae, which therefore, as we have seen, constitute 

 the Sacrum. 



(601 s ) In examining the bones which enter into the composi- 

 tion of the head of the Crocodile, or indeed of most Reptiles, 

 the anatomist finds his studies much facilitated by the circumstance 

 that the sutures separating the individual bones never become 



