tlte Pecloral Girdle in the Pipefish. G19 



first two vertebrae is strengthened by the development of 

 l()nf!:itudinal ridges on the internal aspect of the hone. 

 With the advance of ossification the small processes appear 

 on tlie proximal radials, and the scapula and proximal radials 

 become differentiated from the intermediate cartilage. As 

 the body of the coracoid becomes ossified the vertical limb 

 (fig. l,2}rp') arises as an upward extension from the anterior 

 end, i. e. from the precoracoid process, while the postcoracoid 

 process develops into the posterior half of the horizontal limb 

 ( pt.j))- The arm ossifies with the remainder of the coracoid, 

 but its upper end remains hollow, to give a better attachment 

 to the intermediate cariilage. 



The formation of a practically continuous dermal armour 

 of bony scutes, and its special strengthening to produce a 

 more rigid framework in the pectoral region by the restric- 

 tion of the movements of its individual parts, are closely 

 connected with the development of the pectoral girdle in the 

 pipefish, and are responsible for most of the peculiarities of 

 the adult girdle. 



The clavicle apparently arises as a slender vertical bar in 

 front of the coraco-scapular cartilage, and expands both 

 forward and backward at its upper end, to have a rigid 

 vertebral attachment and to form part of the dermal armour. 



The development of the primary cartilaginous shoulder- 

 girdle presents several peculiar features. The scapular 

 region is small and is primarily limited by a foramen in the 

 cartilage, which apparently rises in conjunction with and in 

 the same way as the three foramina by which the four 

 proximal radials are initially indicated, and with which it 

 forms a seines of four which persists in the adult. There is 

 apparently no other sign of a division of the primary 

 shoulder-girdle into a true coraco-scapular and a radial 

 cartilage. A true scapular foramen is present in the earlier 

 stages, but eventually becomes merged in the large opening 

 between the coraco-scapular cartilage and the clavicle. A 

 scapular process is also present, and persists in the adult 

 us the upper arm of the scapula. The adult scapula becomes 

 distinct from the remainder of the coraco-scapular cartilage 

 by ossifying into a small bone which closely resembles the 

 proximal radials in form and dimensions, as well as in its 

 genesis. The reduction of the scapula and its resemblance 

 to a proximal radial are found in various lesser degrees in 

 the Hemibranchiate fishes, and may be traced through a 

 series of stages ending with Fistnlaria, which presents an 

 arrangement of these parts closely allied to that in Syngnathus, 



