108 TllANSCKNDKNTAL ANATOMY IN ENGLAND 



parts, without their essential homological relationships being 

 thereby obliterated. These relationships are mainly, if not 

 wholly, determined by the relative position and connection 

 of the parts, and may exist independently of form, proportions, 

 substance, function and similarity of development. But the 

 connections must be sought for at every period of develop- 

 ment, and the changes of relative position, if any, during 

 growth, must be compared with the connections which the 

 part presents in the classes where vegetative repetition is 

 greatest and adaptive modification least" (p. 6). It is 

 interesting to note that in Owen's opinion comparative 

 anatomy explains embryology. Thus the scapula, which is 

 the pleurapophysis of the occipital vertebra, is vertical on its 

 first appearance in the embryo of tetrapoda, and lies close up 

 to the head (On tJie -Nature of Limbs, p. 49) the embryo 

 shows a greater resemblance to the archetype than the 

 adult. " We perceive a return to it, as it were, in the early 

 phases of development of the highest organised of the 

 actually existing species, or we ought rather to say that 

 development starts from the old point ; and thus, in regard 

 to the scapula, we can explain the constancy of its first 

 appearance close to the head, whether in the human embryo 

 or in that of the swan, also its vertical position to the axis of 

 the spinal column, by its general homology as the rib or 

 'pleurapophysis' of the occipital vertebra" (Limbs, p. 56). 



We owe to Owen the first clear distinction between 

 " homologous" and " analogous " organs ; it was he who first 

 proposed the terms " homologue " and "analogue," which he 

 defined as follows : " Analogue. A part or organ in one animal 

 which has the same function as another part or organ in a 

 different animal." " ! foniologue. The same organ in different 

 animals under every variety of form and function." 1 



Me introduced also useful distinctions between Special, 

 ( u neral,und Serial Homology. " The relations of homology," 

 he writes, "are of three kinds : the first is that above defined, 

 viz., the correspondency of a part or organ, determined by its 

 relative position and connections, with a part or organ in 

 a different animal ; the determination of which homology 

 indicates that such animals are constructed on a common 

 1 I. <\ lures on Inrcrtclnate Animals, pp. 374, 379, 1843. 



