ON THE OUTLOOK OF VERTEBRATE MORPHOLOGY. 77 



more especially the incorporation of one or more differ- 

 entiated vertebral segments, or at least their associated 

 arches, in the skull, is apparently the rule — the so-called 

 occipital articulation being inter-vertebral. In view of these 

 facts, and others, well known, involving variation of the occi- 

 pital and anterior-vertebral regions of the axial skeleton, the 

 taxonomic value in the past attached to the presence of a 

 single or double condyle is materially lessened, if not nullified. 

 The mention of the last-named topic leads up naturally 

 to a consideration of the Mammalia, believed by some to 

 be most nearly allied to the Reptiles and by others to the 

 Amphibia. The classical researches of Gcette 32 have, 

 within the last twenty years, laid the foundation for a 

 complete reconciliation between the distinctive features of 

 the shoulder-girdle in Mammals and certain Reptiles. The 

 inter-clavicle, originally thought to be formed in Mono- 

 tremes alone among Mammalia, has been found to appear 

 during development in the Placentalia ; and the segmenta- 

 tion of the coracoid into superposed epi- and meta-cora- 

 coidal elements has been observed in representative 

 members of the leading orders of Placental 33 Mammals. 

 The marked differences between the adult condition of 

 the hip-girdle of Ornithorhynchus and that of all other 

 mammals have been found to be due to change 

 occurring late in ontogeny; 34 and the discovery of 

 the independent development of epipubic supports for 

 the abdominal wall in the Amphibia, Reptilia, and Mam- 

 mals, 35 has lessened the value of these as guides to affinity 

 to the utmost. Both in respect to their fundamental 

 constitution and disposition, the limb-girdles of mammals 

 and certain of the anomodont reptiles stand now agreed 

 and alone. That these resemblances are indicative of 

 mere convergence by independent modification, rather than 

 of a direct genetic relationship, might well appear, by 

 analogy to Haacke 36 and Giacomini's 37 discovery of the 

 independent acquisition of true vitelline and allantoic 

 placentas of the mammalian type by the Scincoids. That 

 they are not so, however, is most certain, from the fact 



