STERNUM. 563 



before backwards, and thus give rise to two cartilaginous bands. 

 These bands become segmented off from the ribs with which 

 they are at first continuous, and subsequently fuse in the median 

 ventral line to form an unpaired sternum. The Mammalian 

 presternum (manubrium sterni) and xiphosternum have the 

 same origin as the main body of the sternum (Ruge, No. 438). 



In the Amphibia there is no structure which admits from its 

 mode of development of a complete comparison with the 

 sternum of the Amniota ; and it must for this reason be 

 considered doubtful whether the median structure placed behind 

 the coracoids in the Anura, which is usually known as the 

 sternum, is really homologous with the sternum of the 

 Amniota 1 . 



The remaining Ichthyopsida are undoubtedly not provided 

 with a sternum. 



BIBLIOGRAPHY of Ribs and Sternum. 



(430) C. Claus. " Beitrage z. vergleich. Osteol. d. Vertebraten. I. Rippen u. 

 unteres Bogensystem. " Sitz. d. kaiserl. Akad. Wiss. IVien, Vol. LXXIV. 1876. 



(431) A. E. Pick. "Zur Entwicklungsgeschichte d. Rippen und Querfort- 

 satze." Archiv f. Anat. und Physiol. 1879. 



(432) C. Gegenbaur. "Zur Entwick. d. Wirbelsaule des Lepidosteus mil 

 vergleich. anat. Bemerk.'' Jenaische Zeit., Vol. in. 1867. 



(433) A. Gotte. "Beitrage z. vergleich. Morphol. d. Skeletsystems d. Wirbel- 

 thiere Brustbein u. Schultergiirtel." Archiv f. mikr. Anat., Vol. xiv. 1877. 



(434) C. Hasse u. G. Born. " Bemerkungen lib. d. Morphologic d. Rippen." 

 Zoologischer A nzeiger, 1879. 



(485) C.K.Hoffmann. "Beitrage z. vergl. Anat. d. Wirbelthiere." Niedcr- 

 land. ArcJm' Zool., Vol. IV. 1878. 



(436) W. K. Parker. " A monograph on the structure and development of the 

 shoulder-girdle and sternum." Ray Soc. 1867. 



(437) H. Rathke. Ucb. d. Ban u. d. Entwicklung d. Brustbcins d. Sauricr. 



i853- 



(438) G. Ruge. " Untersuch. iib. Entwick. am Brustbeine d. Menschen." 



Morphol. Jahrbuch., Vol. VI. 1880. 



1 The so-called sternum of the Amphibia develops in proximity with certain 

 rudimentary abdominal ribs, and Ruge has with some force urged (against Gotte) 

 that it may be for this reason a rudimentary structure of the same nature as the 

 sternum of the higher types. 



362 



