AMPHIBIANS. 79 



Example 6. Rana temporaria, Linn. 



Plate V, figs. 1 14 show the modification undergone by the Shoulder-girdle and Sternum 

 from the time when the hind-legs have appeared (the fore-legs being hidden behind the oper- 

 cular folds) to the perfectly adult condition. 



First stage, Rana A. The tail was full-sized in this stage, and the fore-legs, although folded up, 

 were developing fast ; the hind-legs were small, but very evident, and the long, flat-spiral coil of 

 intestine undiminished in length and volume : thus the Tadpole was very distended in its short, 

 abdominal region, and the visceral laminae, which had met long before, were of extreme tenuity. 

 The Shoulder-girdle moieties at this stage are scarcely relatively larger than they are in the 

 Osseous Fishes, notwithstanding the large size of the supra-scapula (fig. 1, s. sc.), the point 

 of which does not reach the vertebral region ; whilst, below, the distance to the mid-line (see 

 the dotted lines in fig. 1) is very great. 



The relation of the upper point of the supra-scapula at this stage is shown in fig. 2 ; it 

 corresponds to the intercentrum between the second and third vertebrae, and has no more relation 

 to the occiput than the same part in Osseous Fishes. This very minute Shoulder-girdle, which is 

 magnified twenty-five diameters (see fig. 1), has nearly all the persistent characters of that of the 

 adult Frog ; for ectostosis has begun in all the four normal regions ; and, whilst from the first the 

 scapula? andcoracoids (fig. 1, sc., cr.) are enringed with this thin, almost structureless, calcareous 

 film, the deposit forming the outer-bone' of the supra-scapula (s. sc.) and prae-coracoid (p. cr.) 

 is a two-edged plate, clamping the front of its cartilaginous model ; and, as is normal, it is larger on 

 the outside than on the inner face. The supra-scapula at present is twice as high as it is broad, 

 and is like a broad knife with a sinuous back, and a convex edge ; this edge is the posterior 

 margin. There is a short handle to this knife, broader above than below, and rather constricted 

 at the middle : it is not much flattened : this is the scapula (sc.), and is much more than its 

 own length from the prae-coracoid. The massive glenoidal region (gl.) is all soft, and the cavity 

 is a good distance from the scapula above and the coracoid below. This " cup " is very 

 elongated, and has, at the middle of its outer edge, a very cleanly cut notch ; near it I have 

 shown the head of the humerus (h.), which is already well developed. The cartilage is very 

 bulbous, both in front and below the glenoid cavity, and then the Shoulder-plate is somewhat 

 constricted at both sides, and dilates, so as to produce distinct angles below. This region is 

 cloven into a flat anterior, and a narrower, rounded posterior bar by the coracoid fenestra (cr. f.), 

 which is accurately egg-shaped in outline, the narrow end being above. Flanking the anterior 

 bulbous part, and clamping the broader anterior bar, is the thin, two-edged, prae-coracoid plate 

 (p. cr.) ; and ensheathing the rounded bar behind is the coracoid (cr.), which is much like the 

 scapula, but not half the size. The crescentic, flat, broad bar bounding the fenestra below, and 

 running into both coracoid and prae-coracoid, is the soft epicoracoid (e. cr.). There could 

 be seen no mark of the cleft which afterwards splits the scapula below, so that at present 

 there is only the coracoid cleft, imperfect at both ends, dividing the continuous cartilage; 

 for the appearance of division between the scapula and supra-scapula is quite a deception. 

 Plate V, fig. 14 shows this part of fig. 1 magnified one hundred diameters ; ec. o. is the 

 ectosteal scapular sheath ; c., the cartilage passing into the supra-scapular region, and pr. the 



