THE PECTORAL GIRDLE. 605 



Amphibia. In Amphibia the two halves of the shoulder girdle are 

 each formed as a continuous plate, the ventral or coracoid part of which is 

 forked, and is composed of a larger posterior and a smaller anterior bar-like 

 process, united dorsally. In the Urodela the two remain permanently free 

 at their ventral ends, but in the Anura they become united, and the space 

 between them then forms a fenestra. The anterior process is usually (Gegen- 

 baur, Parker) regarded as the praecoracoid, but Gotte has pointed out that 

 in its mode of development it strongly resembles the clavicle of the higher 

 forms, and behaves quite differently to the so-called prsecoracoid of Lizards. 

 It is however to be noticed that it differs from the clavicle in the fact that it 

 is never segmented off from the coraco-scapular plate, a condition which has 

 its only parallel in the equally doubtful case of the Chelonia. Parker holds 

 that there is no clavicle present in the Amphibia, while Gegenbaur maintains 

 that an ossification which appears in many of the Anura (though not in the 

 Urodela) in the perichondrium on the anterior border of the cartilaginous 

 bar above mentioned is the representative of the clavicle. Gotte's obser- 

 vations on the ossification of this bone throw doubt upon this view of Gegen- 

 baur ; while the fact that the cartilaginous bar may be completely enclosed 

 by the bone in question renders Gegenbaur's view, that there is present both 

 a clavicle and praecoracoid, highly improbable. 



No interclavicle is present in Urodela, but in this group and in a number 

 of the Anura, a process grows out from the end of each of the bars (prae- 

 coracoids) which Gotte holds to be the clavicles. The two processes unite 

 in the median line, and give rise in front to the anterior unpaired element of 

 the shoulder girdle (omosternum of Parker). They sometimes overlap the 

 epicoracoids behind, and fusing with them bind them together in the median 

 line. Parker who has described the paired origin of the so-called omosternum, 

 holds that it is not homologous with the interclavicle, but compares it with 

 his omosternum in Mammals. 



BIBLIOGRAPHY. 



(463) Bruch. " Ueber die Entwicklung der Clavicula uncl die Farbe cles 

 Blutes. " Zcit.f. wiss. Zool., iv. 1853. 



(464) A. Duges. " Recherches sur 1'osteologie et la myologie des Batraciens a 

 leurs differens ages." Mcmoires des savants etrang. Academic royale dcs sciences de 

 Finstitiit de France, Vol. vi. 1835. 



(465) C. Gegenbaur. Untersuchungen zur -vergleichenden Anatomie der Wir- 

 belthiere, 2 Heft. Schultergilrtel der IVirbelthiere. Brustflosse der Fische. Leipzig, 

 1865. 



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

 thiere : Brustbien u. Schultergiirtel. " Archivf. mikr. Anat. Vol. xiv. 1877. 



(467) C. K. Hoffmann. "Beitrage z. vergleichenden Anatomie d. Wirbel- 

 thiere." Niederlandisches Archivf. Zool., Vol. V. 1879. 



(468) W. K. Parker. "A Monograph on the Structure and Development of the 

 Shoulder-girdle and Sternum in the Vertebrata." Ray Society, 1868. 



