144 ANURA CHAP. 



holes for the spinal nerves. Hymenochirus has consequently 

 only 5 presacral vertebrae, the vertebral column being shortened 

 to the greatest extent known amongst Vertebrate* For further 

 information see p. 22. The ilia are much broadened vertically, 

 and are firmly attached to the sacrum. The shoulder -girdle 

 is sometimes described as of the arciferous type, but this is quite 

 unjustifiable. The epicoracoid cartilages do not overlap each 

 other, but meet, and partly fuse in the middle line. The 

 three genera exhibit some differences. In Pipa and Hymeno- 

 chirus the bony portions of the coracoids are much expanded 

 dorsally, and there is a considerable amount of epicoracoid 

 cartilage, that of the precoracoid bars extending backwards as 

 a broad-based and blunt omosternum. Xenopus is devoid of 

 an omosternum, and the configuration of the whole apparatus 

 is more slender. The metasternum of Xenopus and Hymeno- 

 chirus broadens out laterally. Hymenochirus greatly resembles 

 Breviceps, a genus of Engystomatinae, in the relative position 

 and size of the various parts of the shoulder -girdle and 

 sternum. 



The tibio-fibula of Hymenochirus has a wing-like expansion of 

 thin bone on each side, forming a deep groove on the outer aspect. 

 The astragalus and calcaneum are united by a similar bony 

 expansion with wing-like projections. 



The lungs are remarkable for the prominent development of 

 trabecular projections and niches, so that their free lumen is 

 much restricted; they have thereby reached a much higher 

 stage than in any other Amphibia or even many Autosauri. The 

 persistence of an arteria sacralis s. caudalis, a vessel absolutely 

 absent in the adult Rana, is a primitive feature, and the same 

 applies to the presence of a true first spinal or suboccipital 

 nerve. 



The skin of the back and belly is supplied by two great 

 branches from the arteria anonyma, one arising proximally, the 

 other distally from the subclavian ; herewith is correlated the 

 almost complete absence of the arteria cutanea magna, which as a 

 branch of the ductus pulmo-cutaneus plays such a prominent 

 role in the other Anura. Only in Pipa, but not in Xenopus, is the 

 great cutaneous vein represented by a very small branch. Both 

 these genera possess a much more complicated " diaphragm " than 

 the other Anura, chiefly owing to a special muscle which arises 



