DEVELOPMENT OF PELViC GIRDLE IN THE CHICK. 17 



far on the way to becoming adult cartilage. At first the whole 

 structure progresses uniformly, except that the girdle always 

 lags a little behind the femur, but passes off gradually into it. 

 The " prechondral elements " and a small quantity of cartila- 

 ginous matrix exist across the future line of division, which, 

 however, develops no further, but retrogrades into the fibrous 

 tissue of the joint. 



Fig. 7 represents a further advance of the girdle towards the 

 adult form. 



In later stages, no important changes take place. The 

 anterior branch of the pubis, which is always rather behind 

 the rest of the girdle in histological development, becomes 

 more and more proportionately insignificant, and forms at last 

 the pectineal process of the pubis. The posterior branch of 

 the pubis becomes very slender. Both it and the ischium 

 grow more and more backwards, passing through the stage 

 permanent in such forms as Apteryx (where they are much 

 curved, and their long axes are inclined at an acute angle to 

 the long axis of the ilium) to the stage found in the adult fowl, 

 where the pubis and ischium — except the most proximal por- 

 tions of them — are straight, and point directly backwards, so 

 that the long axes of all three bones are parallel to one another. 



Ossification begins comparatively late, i. e. later than in the 

 limb. For a long time there is a cartilaginous continuity of 

 the three elements round the acetabulum. The bones gradu- 

 ally grow up to and surround the acetabulum. Cartilage 

 remains also at the free ends of the bones for a long time. A 

 day or two before hatching (see fig. 18), the acetabulum is 

 surrounded by bone, except for a small region of its front wall, 

 continuous with the likewise cartilaginous anterior branch ot 

 the pubis. The position and relations of this latter element, 

 together with the fact of its remaining cartilaginous so long, 

 remind one to some extent of the cartilage found in a similar 

 situation in the Crocodile embryo after the rest of the girdle 

 has ossified. According to Hoffmann,' this cartilage is homo* 



1 Ci K. Hoffmann, " Beitrage zur Kenntniss des Beckens der Amphibieu 

 und Reptilien," 'Nied. Archiv f. Zoologie,' Band iii, 1876. 



