PEDIGREES AND RELATIONSHIPS 17 



the form of the Theriodontia, the ancestors of mammals, and 

 are characterised, among other features, by the opening-up of 

 the temporal region of the skull, with, as already mentioned, 

 the formation of a single temporal arcade, which, however, at 

 least in some cases, as Cynognathus^ for example, consists of 

 two elements. 



To describe in detail the mammalian features presented by 

 the anomodonts and other Theromorpha, or indeed the general 

 characteristics of that subclass, would be out of place on the 

 present occasion. It ma)' be mentioned, however, that the 

 skull, with the exception of the retention of a quadrate, a com- 

 pound lower jaw, and a prefrontal bone (which is a character- 

 istic reptilian feature) in many cases might almost be described 

 as that of a mammal. The reduction in the size of the quadrate 

 and of the posterior elements of the lower jaw in this group 

 has been already noticed. In the theriodont, or carnivorous, 

 section of the anomodonts, as exemplified by Cynognathus and 

 Galecynus, the teeth recall those of carnivorous mammals. The 

 shoulder and pelvic girdles are also essentially of the same type 

 as those of the monotreme, or egg-laying, mammals, and present, 

 moreover, a remarkable serial homology ; that is to say, the 

 three elements of the one (scapula, epicoracoid, and coracoid) 

 correspond almost exactly with those of the other (ilium, pubis, 

 and ischium) while the obturator foramen, or perforation between 

 the pubis and ischium is an essentially mammalian feature. 

 Nor is this all, for the theromorph shoulder and pelvic girdles 

 are essentially unlike those of other reptiles, this being especially 

 the case with the pelvis, in which among many reptiles, such as 

 dinosaurs, the pubis and ischium, are long divergent rods. 



The humerus, or upper arm-bone, is also essentially like 

 that of the lower mammals, having a strongly developed deltoid 

 or radial crest in its upper half, and a perforation (entepi- 

 condylar) on the inner, or ulnar, side of its lower extremity. 

 Not less important is the fact that the number of joints in the 

 toes, at least in several cases, is the same as in mammals ; while 

 it would seem that, as in that group, the ankle-joint was situ- 

 ated between the tibia and fibula and the first row of the 

 tarsus. 



In concluding these observations on the relations between 

 reptiles and mammals, the following passage from a paper 



2 



