tl28 BARON NOPCSA ON THE [Feb. 19, 



volant, and began to fly by force — that is, move its patagium, 

 — the sternum must evidently have developed a sternal crest, 

 the patagium must have continued to increase its surface, and 

 this then would not only produce stretching of the limbs but also 

 development of secondary supports of the patagium. 



Svich secondary supports are, as we shall see, developed at 

 different times and in different ways, being produced by special 

 development of the oleci'anon, the carpal bones, and ossified 

 tendons. In the long-tailed Pterosaurs such supports are absent 

 in the fore limb ; in the short-tailed Pterosaurs, however, they are 

 well developed and are represented by a modified cai-pal which, 

 according to Williston, shows {Pterodactylus — Nyctodactylus) 

 progressive evolution. Another modification that each patagium 

 produces in the animal's body is to bring all the radial supports 

 to the same level, and this, making the acetabulum and knee 

 rotate outward and backward, produces subsequently crawling 

 locomotion. 



When the last stage of development is attained and aerial 

 locomotion accomplished by skill and not by force {N'yctodaGtyhis, 

 Eha'niphorhynchus)^ the patagium obviously not only wovild assume 

 a pointed outline and become reduced to a smaller surface, but in 

 some cases also the tail would change to a rudder-like organ 

 [Rhamphorhynchus) or become entirely lost, while the attenuated 

 feet would in this case assume the function of steering (Nycto- 

 saitrus). It is of no small importance that of the two highly 

 specialised groups of Pterosaurians(Ilhamphorhynchida3 andl^ycto- 

 sauridse) the tailless ones should have survived the longer. 



Mammals. 



Very much the same changes as are to be found between 

 Tribelesodon, Dimorphodon^ and Rhamphorliynchus on the one 

 hand, and Pterodactylas and Nyctodactylus on the other, are also 

 to be observed when we come to consider the patagium-flying 

 Mammals. A set of good diagrams of flying mammals has recently 

 been published by R. S. Lull. Petaurus and all other animals 

 with a small patagium represent the stage where, as in all arboreal 

 animals, a very long tail is present. 



Only a plagiopatagivim is present in Petaurus, a propatagium. 

 is added in Pteromys, whilst in Anomcdurtbs even a uropatagium 

 is present. As in Pterosaurs, supplementary patagial supports ai-e 

 frequently developed. In Anomcdurus and Vespertilio svich a 

 support arises from the olecranon, in Pteromys it is partially 

 attached to the pisiforme and partially, though to a less extent, 

 to the 5th metacarpal ; and in embiyos of Ohiroptera quite a 

 similar structure is met with : a modification recalling the back- 

 wardly directed toe of the hind leg in Ditnorphodon is produced 

 by the development of the calcaneum's calcar projection. As in 

 Pterosaurs, so also in flying Mammals a very low ilium is present, 

 and this not only in Chiroptera but also in Galeopithecus, where. 



