DEVELOPMENT OP PELVIO GIRDLE IN THE OIIIOK. 



409 



Reptiles. 



I. Pubis 



2. Processus 

 lateralis pu- 

 bis 



Dinosaurs. 



Anterior branch 

 of pubis 

 (' pubis ' of 

 Marsh) 



Pubis (' post- 

 pubis ' of 

 Marsh) 



Embryo Bird. 



Birds. 



Anterior branch Pectinal pro- 

 of pubis cess of pubis 



Posterior branch Pubis 

 of pubis 



Mammals. 



Pectinal pro- 

 cess of pubis. 



Pubis. 



The development of the skeleton of the limb has 

 been described by Gegenbaur.^ Rosenberg," has supplemented 

 Gegenbaur's accounts by his discovery of the fifth metatarsal, 

 and quite recently Baur ^ has published a paper on the Tarsus 

 of Birds and Dinosaurs. The results of my work on the 

 development of the bird's tarsus agree with Baur's in almost 

 every detail, so that I will give only a short account of it. 



In a five days' chick (see fig. 1) the tissue of the limb is 

 condensed axially into a single mass, about three times as long 

 as it is broad, and extending through the proximal half of the 

 limb. The skeleton is produced by the subsequent elongation 

 and segmentation of this mass. 



On the sixth day (length of hind limb 0*14 in., see fi^-. 8) 

 we can recognise all the chief elements of the skeleton, thouo-h 

 they are completely continuous. The tarsus forms a broad 

 transverse band, continuous with the tibia and fibula above, 

 and with the metatarsals below. Five metatarsals are present, 

 the first and second being rather closely united. The tiiird is 

 the longest and the fifth the shortest. No cartilaginous 



1. C. Gegenbaur, " Vergleich.-Aaut. Bemerkungcn iiber das Pussskelet der 

 Vogel," 'Archiv fiir Anat. uud Pliys.,' 18G3 ; and " Untersuchuugou zur 

 vergleicheudeu Auatoniic der Wirbelthicre," i Heft, ' Carpus uud Tarsus ' 

 lS6i. 



2 A. Rosenburg, " Ueber die Entwicklung des Extremitaten-Skelets bei 

 einigen Wirbelthieren," ' Zeitschrift f. wiss. Zoologie,' 1873. 



3 G. Baur, " Der Tarsus der Vogel uud Diuosaurier," ' Morphologisches 

 Jahrbuch,' Band viii, Heft iii, 1882. 



