1 86 



NA TURE 



\_yan. 8, 1874 



7 HE COMMON FROG* 

 VIII. 



THE skeleton of the ankle as developed in the frog's 

 class presents us with some characters, which, 

 more than even those of the wrist, suggest the pas- 

 sage of the hne of affinity directly from Batrachians to 

 mammals, leaving both reptiles and birds on one side. 



Fig. 51. Fig- S^- 



Fio, 51.— Right foot of Emeu, a, astragalus; d,—di, second, third, and 

 tnurth d.gits ; }n metatars'ls anchylosed together except at their distal 

 ends : / tibia ; t^, distal tarsal element. 

 Fig. 52— Left foot of a Monitor Lizard (FaraniM). /, 6bula ; «/■— w:5, the 

 five metatarsals, w' being that of the hallux ; t> tibia ; i, astragalo- 

 cuboides ; 3, ecto-cuneiforme. 



In the first place we meet in the frog with certain extra 

 ossicles in the inner side of the foot, which present the 

 appearance of a broad rudiment of an extra digit on the 

 inner side of the great toe. Now we find a structure very 



I'IC. 53. flG. 54. 



Fig. 53.— Skeleton of posterior extremity of an eft. 



Fig. 53. — Bones of foot of Frog. — a, astragalus : c, OS calcis : ac, united por- 

 tions of these bones ; //, extra ossicle of inner side of foot ; cb^ ossicle 

 representing cuboid and other tarsal bones — 1, 2, 3, 4, 5 — the five meta- 

 tarials. 



similar in form in animals remote enough from Batra- 

 chians, yet rarely do we find such in any intermediate 

 kinds. Thus in certain tree-porcupines the ankle is fur- 

 nished in like manner — another instance of the inde- 

 pendent origin of strikingly similar structures. 



* Conliiuied from p. 150. 



There are other matters, however, more important than 

 this. It has been remarked that the wrist shows an 



Fig. 55.— The Maholi Galago. 



amount of resemblance to the same part in beasts which 





Fig. 56. — Elongated tarsus of Lemuroids. Left-hand figure, tarsus of 

 Clteirogaleus ; right-hand figur?, tarsus of Tarsius. A. caicaneum ; B^ 

 cuboides; C, naviculare. 



is wanting in most reptiles and in all birds. The same 



Fic. 57.— Tadpole of Bull Fro?, partly dissected, to show the muscles of the 

 tail and the branches of the 8th nerve or the vagus, a, great lateral 

 brahch giving off— -^, a dorsal branch, and c, the lateral branch (or neruns 

 lateralis) ; d, branches descending and passing along the branchial 

 arches. The descending branches seen behind the branchial nerves on 

 the side of the belly are not branches ot the vagus at all, but spinal 

 nerves, which come out from beneath the muscles and pass down under 

 the tisri'us lateralis, and without having any communication with it. 



observation may be repeated with far greater force as 

 regards the ankle. 



