THE HUMAN STERNUM 51 



B. Amphibia 



Among Amphibia wide variations exist in the shoulder-girdle and 

 sternum. In some examples, as in Proteus anguinus, a fish-like character 

 persists. Praecoracoids and coracoids are present, but no sternum. In 

 others, as in Bufo, a leaf-like sternum is present between the ventral ends of 

 the shoulder-girdles. In other cases again, as in Rana (PL VIII, Fig. 57), 

 an additional element, the omosternum, makes its appearance, separated 

 from the sternum proper by the praecoracoids, epicoracoids, and coracoids. 

 Neither omosternum nor sternum have any connexion with the ribs : but 

 as shown already are derived from the shoulder-girdle, and are in intimate 

 association with it. 



C. Reptiles 



Among reptiles there are many difFerences in the condition of 

 shoulder-girdle, sternum, and ribs, and in their relations to one another. 

 There is, however, a distinct gradation as we proceed from lower to higher 

 forms. 



Among Ophidia, in which the limbs and their girdles are absent, the 

 sternum is absent too ; and at the same time the ribs are highly developed 

 and of great importance. 



In Chirotes canaliculatus, ' the only annulate saurian with anterior 

 limbs,' there is together with a shoulder-girdle, a sternum which is differen- 

 tiated into presternum, mesosternum, and metasternum (PI. VIII, Fig. 58). 

 'The ribs do not appear to be connected with the relatively extremely small 

 bone ' (Parker). 



In Anguis fragilis, clavicles, interclavicle, and articulating coracoids are 

 present, together with a presternum, connected by fibrous tissue with one 

 pair of ribs (PI. X, Fig. 6^). 



In such reptiles as Iguana tuhenulata and Lemanctus longipes, clavicles, 

 interclavicle, precoracoid, and coracoid, are closely associated with a broad 

 shield-like sternum. In Lemanctus longipes (PL VIII, Fig. 59), there are 

 eight cervical vertebrae, of which the last four carry ribs. Beyond these 

 there are four sternal ribs, i.e., vertebral ribs, articulating by synovial joints 

 with the lateral borders of the sternum. There is no differentiation of 



