4 EDWARD S. MORSE ON 



the fibula, is a Dinosaurian character met with to some extent among birds, but quite as 

 well marked in mammals. Secondly, the shape of the distal end of the bone is birdlilve ; 

 but that form is found in no adult bird, and is only to be detected in the young 

 bird before the tarsus had become blended with it, so that while it might go to show, 

 perhaps, that birds are descended from a common stock with Dinosaurs, it would be 

 misleading to regard it as altogether avian, since the character is lost in the adult bird's 

 skeleton" (page 57). And furthermore, he says, "But when the tarsus, or rather, the 

 astragalus, is closely applied to the tibia, as in Megalosaurus, Poecilopleuron, Laelaps, 

 or lo-uauodon, it gives the bone a resemblance to the birds which is almost convincing, 

 since the parallel extends to nearly every detaU. The character, however, is shorn of 

 much of its importance, when we remember that there are many Dinosaurs in which 

 there is an os calcis, or heel-bone, placed side by side with the astragalus." 



Professor Seeley is aware that in Laelaps the hour-glass shaped tarsal bone represents 

 the OS calcis and astragalus connate ; also that Prof. Cope shows that these two bones are 

 ankylosed in Ornithotarsus. 



The memoir of Gegenbaur on the Tai'sus and Carpus of Birds had, for the moment, 

 probably escaped the attention of Prof. Seeley. In this contribution of Gegenbaur's the 

 separation of the tarsal portion into two bones, the upper and iinder tarsal bone, is clearly 

 pointed out. Furthermore, Gegenbaur shows two centres of ossification in tlie upper, 

 or proximal bone, which he rightly infers to represent the tibiale and fibulare (these 

 names are used in preference to those of astragalus and os calcis, as better defining the 

 relations existing between them and the tibia and fibula). These demonstrations were 

 based on an examination of the chick at a late stage of embryonic growth. 



In my memoir (8), on the Tarsus and Carpus of Birds, I not only fully confirmed 

 the observations of Gegenbaur, but showed the absolute separation of these two 

 elements as tibiale and fibulare, based on an examination of a number of species of birds 

 at an earlier stage than those examined by Gegenbaur. Figures of these were also given, 

 showing the fibula, with the same length as the tibia, and nearly api^roximating to the 

 fibulare. 



While preparing the memoir above alluded to, Prof. Wyman kindly sent me some 

 observations of his on the tarsus of the embryo Heron, which he generously allowed me 

 to incorporate ■\\dtli my paper. Briefly, these consisted in his finding a long style- 

 shaped bone, broadest at its distal extremity, lying in front, and at the distal end of the 

 tibia, which he believed to represent the so-caUed ascending process of the astragalus, 

 but which was shown to have an independent centre of ossification in the embryo, and 

 to remain free from the other tarsal bones till the young had left the egg ; when 

 it appeared attached to the coessified tibiale and fibulare, and presented the appearance 

 not unlike that shown by Huxley in the young ostrich. 



My interpretation at the time was that this new tarsal bone represented the inter- 

 medium, a tarsal bone which is clearly seen in the salamanders as ocoupying a position 

 between the tibia and fibula, and indeed with half its length forced uj), as it were, between 

 these two bones. 



I have previously shown that as the proximal series of tarsal bones became united, the 

 fibida diminished in size proportionally with the rapid increase of the tibia, and became 



