OCR Text |
Show 1893.] OF THE TERRESTRIAL VERTEBRATA. 591 my own specimen this ligament is superficially calcified, and the acromion is vertically enlarged at its point of origin, in a manner suggestive of a tendency on the part of this bar to fulfil the function of the overgrown epicoracoid of Choloepus, Bradypus, and other genera. In Choloepus the two conditions coexist. I have long desired to work out the detailed anatomy of the Edentate axilla in its bearings on these facts, but the necessary fresh material has not been obtainable. I cannot help thinking, however, that they point to the conclusion that the condition of the coraco-scapular apparatus in Bradypus which Mr. Lydekker has described is due to one of a series of adaptive changes which that of the Edentata has undergone in relation to the modification of their fore limb and pronounced peculiarities of life. Certain it Eig. 2. The blade-bone of Cycloturus didactylus. 2 a, from the side ; 2 b, from the front. X 1^. ac. Acromion, co. Coracoid process, lg. Acromio-scapular ligament. is, that, except for the joint possession of a bicoracoid, the resemblances between the Edentate and Dicynodont blade-bones are indicative of nothing but a parallelism of adaptive change; and it is interesting to meet with this in two great groups of animals the ancestors of which we to-day seek independently among the lower Anomodontia. I. append a list of those Placentalia in which I have observed the metacoracoid, and have much pleasure in tendering m y thanks to Mr. Oldtield Thomas, of tbe Natural History Museum, and to Prof. C. Stewart and M r . R. H . Burne, of the Royal College of Surgeons, for permission to examine the collections under their charge. E D E N T A T A . Bradypus cuculliger, Myrmecophaga, Tamandua tetradactyla, Tatusia novemcincta.-UNGULATA. Cervulus reevesi, Equus.-RODENTIA. Ccelogenys paca, Lepus cuniculus, L. timidus, |