CONNECTED WITH THE SHOULDER-JOINT. 127 



that which explains their oneness by a reference to ! genetic affinity.* 

 As to which of the two theories a man will take for his guide in 

 research, so far as any theory can serve for a guide in research, 

 much will depend upon the idiosyncrasies, original or acquired, of 

 individual minds. But though the theory may have only a sub- 

 jective, the facts have an objective cogency. 



With regard to the serial homologies of the fore and hind limbs, 

 and, first, with regard to the representation of the ulna by the 

 fibula and of the radius by the tibia, I have much pleasure in 

 referring to Professor Pagenstecher's views, inasmuch as with many 

 other of his conclusions I cannot bring myself to agree. But any- 

 body who will look at his figures of the bones of the human arm 

 and leg, placed side by side, each in the position which best shows 

 their homotypical relationship, will have good reason for acquiescing 

 in the view stated in the following sentence. In those figures we 

 have the limb in either case so flexed as to have the angle formed 

 at the knee and elbow respectively pointing upwards ; the fore-arm 

 is supinated, and the hand segment hyper-extended, so as to make 

 almost a right angle with the long axis of the fore-arm. The ulna 

 then lies and is directed a little posteriorly and dorsally as regards 

 the radius ; and the thumb and great toe, as also the little finger 

 and the little toe, occupy, severally, corresponding positions. A very 

 similar position, I may observe, is instinctively assumed by a man 

 when he uses his pectoral muscles for the purpose for which quad- 

 rupeds ordinarily employ them, viz. for raising and supporting 

 the trunk upon the fore limbs. And an observation of the position 

 assumed by a man who puts himself into a quadrupedal posture for 

 the purpose of drinking at a stream, or who raises himself by the 

 help of his arms from a low seat by placing his hands on the table 

 at which he is sitting, will illustrate the relations of the extensor 

 and flexor, and of the inner and outer aspects of the two limbs, as 

 well as the most detailed parallelisation of the skeletal elements. 



Secondly, a study of Mr. Parker's descriptions and histories of 

 the shoulder-girdle will leave no doubt on the mind of any one, 

 I apprehend, as to the serial homology of the coracoid with the 

 ischium, and of the praecoracoid with the os pubis. The shoulder- 

 girdles of the frog and the chelonians are especially instructive 

 when compared with the pelvic girdle of the crocodiles. Express 

 utterances as to the relationship of the two sets of bones may be 



