the Pectoral Girdle in the Pipejish. 615 



Museum. In this stage the post-temporal has not yet 

 appeared, but the clavicle already gives an indication of its 

 final shape. It has somewhat the form of an inverted L, 

 consisting of a thin laminar upper part and a slender stem. 

 The laminar upper part is attached by an intervening mass of 

 fibrous tissue to the transverse process of the first vertebra, 

 and extends forward to near the skull, but does not yet 

 extend back much behind the stem. The stem passes down- 

 ward and finally inward, and terminates above the inner edge 

 of the muscle to the hyoid in a median mass of fibrous 

 tissue which connects it with the jugular plate, the lower 

 angle of the coraco-scapular cartilage, and the clavicle of the 

 opposite side. 



At this stage in the development the cartilaginous part of 

 the shoulder-girdle is still predominant, and consists on either 

 side of a vertical triangular coraco-scapular plate in which 

 the parts are as yet imperfectly differentiated. This carti- 

 laginous plate is slightly concavo-convex, with the convexity 

 outward and the curvature more accentuated behind than iii 

 front. The region of the autero-infenor angle represents 

 the coracoid, and at its vertex the cartilage is continued 

 downward on the inner side of the stem of the clavicle to 

 form the precoracoid process, which terminates beside its 

 fellow in the median mass of fibrous tissue already noted. 

 The postqoracoid process has not yet appeared. The scapular 

 portion is represented by the upper angle of the cartilage, 

 Avhich bears tiie small vertical scapular process. On the 

 anterior border of the cartilage toward the lowest point of 

 the scapular region a small hook of the cartilage projects 

 forward inward and downward, producing a well-defined 

 notch, which is probably the rudiment of the scapular 

 foramen*. In stage II. this notch has disappeared, the 

 structures which passed through it passing round the anterior 

 border of the cartilage as in the adult. 



Toward the posterior margin of the cartilage four foramina 

 which pierce the cartilage in a vertical series indicate the 

 formation of the radial elements. The lowest foramen is as 

 yet small, and is evidently the most recent. The uppermost 

 foramen separates the first proximal radial from the upper 



* Cf. Derjugin, Zeitscbr. f. wiss. Zool. xcvi. (1910). A very similar con- 

 dition of this foramen is presented in the figure of the girdle of an 8 mm. 

 Lophius (p. 699) and also m a 5 mm. Gobius minutus (pi. xxvii. fig. 16). 

 The foramen in this case becomes completed subsequently. In the same 

 figure may be seen another notch lower down on the anterior border of 

 the cartilage, which in the next stage (8 mm., fig. 17) is almost a com- 

 plete foramen bounded above by a hook of cartilage, but eventually 

 disappears again (18 mm., tig. 18j. 



