MUSCLES CONNECTED WITH THE SHOULDER-JOINT. 019 



humeral" of the Crocodile, and that its smaller levator tumuli corresponds as closely, 

 as to its insertion, with the postscapular head of that r< ptilian muscle; and it might 

 seem, therefore, that the larger levator humeri muscle of the Fowl remains without a 

 separate homologue in the lteptile, were not this muscle innervated by the saint sub- 

 claviits nerve as the reptilian epicoraco- humeral, whilst the smaller levator humeri is, 

 together Avith the deltoklcs externus, innervated from the circumflex. To an objector 

 who denies the validity of this argument, and lays stress on the fact that the reptilian 

 muscle has not the sternal factor of the avian pectorali* strumitis, I reply, first, in the 

 Emu a muscle very unmistakably homologous with the fHWCOMeo-scapularit of the 

 Crocodile possesses hut a very small sternal factor; and, -econdly, in the Ostrich 

 (Struthio camelas), which also retains apectoralis secinulus, this sternal factor is aborted 

 and lost. Stages of successive degradation from a highly specialized structural arrange- 

 ment may well serve to guide our judgments in problems such as thes< , if it be inn 

 that the essential elements of a structure are the last which it loses so long as it retains 

 any actual functional power at all. But, thirdly, lower types than e\. n the scaly 

 loricate Reptile may have an epicoraco-humer<d with a sternal factor 



This i^ th 



the Frog, where the epicoraeo-humend, (the " pars clavicularis deltoidei " of Ecker, 

 ' Die Anatomie des Frosches,' p. 97) arises from what Mr. Parker (ShnuldeiM Jirdlc, pp. 79 

 and 80, and pi. v.) has shown to he the prcecomco'v i and the omosteruum. 



With this I close my case for proving that the tpicoraeo-humeral of the Reptik is the 

 homologue of the pectoralis s. levator humeri of the Bird. It is not necessary for the 

 acceptance of this conclusion that a person should accept also the Theory of Progressive 

 Evolution. By speaking of organs as being " homologicali > identical," a person who is 

 either averse to pronounce himself, or anxious to secure a dispassionate considerat ion from 

 all parties, or both, may avoid pledging himself either to the theory which teaches thai 

 they are so hy virtue of the "secret bond" of their "conformity to type," or to that 

 which explains their oneness by a reference to " genetic affinity." As to which of tl I 

 two theories a man will take for his guide in research, so far as any theory can serro for 

 a guide in research, much will depend upon the idiosyncratic, original or acquired, of 

 individual minds. But though the theory may have only a subjective, 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 hav, 

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

 other of his conclusions I cannot bring myself to agree. But anybody who will look at 

 his fi-ures of the bones of the human arm and leg, placed side by side, each m the posi- 

 tion which best shows their homotypical relationship, will have good reason for acqiuea- 

 cino- in the view stated in the following sentence. In those figures we have the limb m 

 either case so flexed as to have the angle formed at the knee and elbow respectively 

 pointing upwards; the forearm is supinated, and the hand segment hypcr^xtended to 

 as to make almost a right angle with the long axis of the forearm. The ulna then he, 

 and is directed a little posteriorly and dorsally as regards the radius ; and the thumb and 

 -rent toe, as also the little finger and the little toe, occupy, severally, corresponding po*- 



