LIASSIC PTERODACTYLES. 497 



resemble Reptiles in the absence, not only of a corpus callosnm, but of a fornix and 

 hippocanipal commissure. The Lyencephala have the hippocampal commissure, but no 

 corpus callosum ; this characterises the Placental Mammalia. Birds differ from other 

 Oviparous Vertebrates in the chalaziferous ovum. The particulars in which Birds differ 

 from all Mammals and agree with Reptiles are comparatively unimportant ones of the 

 skeleton. The occipital condyles [e.g.] are more completely blended or unified than in 

 Cetacea. The tympanic is interposed between the mandible and the mastoid, as in 

 Reptiles.^ 



Two genera of Lyencephalous Mammals retain the osteological character common to 

 Birds and Reptiles of the connection of the scapula with the sternum by the intermedi- 

 ation of a fully developed coracoid, and it is one of several and more important characters 

 disproving any sharp definition of the higher warm-blooded Ovipara, at least, from the 

 Ovo-viviparous or Implacental jMammalia. 



The scapular arch retains, in Pterosauria, its crocodilian simplicity, modified in shape 

 and in the angle at which the scapula meets the coracoid adaptively for the function of 

 flight in the limb suspended thereto. There is, consequently, a close similarity to the 

 same elements in Birds of Plight," but without any trace of the superadded furculum. The 

 articular grooves on the sternum for the coracoids communicate or run into each other at 

 the mid line. The articulation of the corresponding end of the coracoid must be as secure, 

 and yet with as easy a motion, due to a well-turned synovial joint (shown first in 

 Pterodactylus Woodioardi and Pt. simus)^ as in any Bird. The confluence of the 

 scapula with the coracoid seems not to be constant in the order Pterosauria ; and where 

 it has been found, as in BlmorpJiodon and Pterodacfj/lus Fittoni, traces of the original 

 suture are present, as represented in the large Neocomian Pterosauria (PL 10). 



In some specimens of Rlmmpliorliyndim Gemmingi and in BhampJiorhynchi(s lonyicaudus 

 the scapula and coracoid seemed not to have coalesced.* The coalescence is complete and 

 constant (so far as may be inferred from two specimens) in Dimorphodon. 



For the analysis of the characters of the humerus in Pterosauria, I may refer to 

 pp. 448—452, PI. 13. The chief seat of variety is the " radial crest " (PI. 16, 53, b, of 

 present Monograph). In the shape and proportions of this extraordinary process 

 Dimorphodon resembles Pterodactylus more than it does Phamphorhynclms. In the 

 proportions of the humerus to the body there is little diversity in the several species. 



The antibrachium is commonly two sevenths longer than the humerus. It consists 



1 Asa taxonomic character — whatever degree of vahie may be adjudged to it — this mode of connection 

 of tlie lower jaw with the skull gains nothing; by calling the tympanic 'quadrate bone,' or by affirming 

 it to represent the ' incus ' or the ' malleus ' of Mammalia, whichever may happen to be the favourite 

 fancy of the day. 



2 P. 395. 



3 P. 444, pi. 12, figs. 7—12. 

 ■* Von Meyeb, op. cit., p. 18. 



