1883.] and Skeleton of the Hind Limb in the Chick. 



329 



developed independently, and Bunge states that it fuses with the 

 rest of the girdle on about the eighth day of incubation. I find 

 that all the elements of the girdle are continuous with one another 

 at the earliest and all other cartilaginous stages. It is the ossi- 

 fication alone which gives rise to any want of continuity in any 

 part of the girdle. 



On the sixth day, when the pubis can first be recognised as a 

 distinct element, it consists of two branches, an anterior and a 

 posterior. The former is directed forwards and very slightly out- 

 wards ; the latter is rather longer, though no broader than the 

 former, and is directed vertically downwards. In later stages, the 

 anterior branch grows less than the other elements, so that it 

 gradually comes to occupy a quite subordinate position. It forms 

 the pectineal process of the pubis in the adult. In some birds it 

 is absent, while in others, e.g. Geococcyx and Apteryx, it is com- 

 paratively well developed. It is undoubtedly homologous with 

 the pectineal process of the pubis found in many, especially some 

 of the lower Mammals. In Omithorhynchus this process reaches 

 the proportionate dimensions found in the embryo bird (see fig. 4). 



Fig-.l. 



Fig-,2. 



■a.pb 



-II 



,-n 



Explanation of figures. 



Fig. 1. Pelvic girdle of Cyclodus. Fig. 2. Pelvic girdle of young Chick. 

 Fig. 3. Pelvic girdle of Laosanrus. Fig. 4. Pelvic girdle of Ornithorln/ncliu*. 



II. Ilium. Is. Ischium. Pb. Pubis, a. acetabulum, p. 1. pb. processus latera- 

 lis pubis. a. pb. anterior branch of Pubis. P. Pb. posterior branch of Pubis 

 (' Post-pubis' of Marsh.) p.p. pectineal process of Pubis. 



