Sheleton of Common Frog. 39 



symphysis is constituted instead of the more or less horizontal 

 one seen in other Amphibia. Anteriorly to the symphysis thus 

 formed the ilia form a second continuous with it by the apposition 

 of two processes homologous with the praeacetabular spurs of the 

 Gallinae, mentioned at p. 28. 



A similar advantage in point of strength is conferred upon the 

 shoulder girdle of the Anura by the prolongation of the more 

 perfectly developed praecoracoids towards, or to the middle line, 

 and by the somewhat similarly more perfected structure of the 

 sternum posteriorly to the coracoid or epicoracoid symphysis. 



The greater development of the limbs, together with the greater 

 strength of the arches supporting them, compensates for the ab- 

 sence of a swimming tail such as the Urodela possess. The bones 

 of both forearm and lower leg are anchylosed to each other. In 

 the lower limb the tarsal segment is greatly elongated. It consists 

 of two bones, the astragalus and calcaneum, which are connected to 

 each other at either end by epiphyses, but have a wide interval 

 between them for the greater part of their length. 



The following points serve to distinguish the Frog's skeleton from 

 the Toad^s. Its ossa ilii are relatively longer, as also the segments of 

 its lower limb; it is not edentulous; it has an azygos osseous ^omo- 

 sternum' segmented off from its praecoracoids anteriorly in the 

 middle line ; the ossification of the coracoid proper has encroached 

 upon the area occupied by the epicoracoid in the Toad, so that 

 scarcely any of this merely endosteally ossified bone appears in the 

 Frog in the line it occupies so prominently in the Toad from the 

 interspace between the mesial end of the coracoids and the mesial 

 end of the praecoracoids. 



The male Frog differs from the female in having a large ridge 

 developed along the posterior aspect of the humerus from the inner 

 condyle upwards for two-thirds of the length of the bone, and in 

 the appearance at the breeding season of a supernumerary ossicle 

 near the thumb. The scapular arch is stronger in correspondence 

 with these structures than we find it in the female. 

 For an account of the skull of Amphibia, see Professor Huxley, 



Elements of Comparative Anatomy, pp. 213-218. 

 For an account of the shoulder girdle, see Mr. Parker's work On 

 the Shoulder Girdle and Sternum, published by the Ray 

 Society, pp. 58-89. 



