REPORT ON THE MARSUPIALIA. 149 



With the first part of this hypothesis I am inclined to agree, viz., that the inner- 

 vation of these muscles points to their probable derivation from the extensor muscles of 

 the thigh ; but I cannot accept the second part of the theory, that the muscles thus 

 derived are replaced by others similarly situated and similarly attached. It is much 

 more reasonable to suppose that the distribution of the peroneal nerve is gradually 

 extended so as to include these muscles ; that, in fact, the peroneal nerve invades the 

 territory of the anterior crural in the same manner as we have seen the external plantar 

 nerve encroach upon the domain of the internal plantar. 



In the nervous arrangements in the hind-limb of the Thylacine and discus there 

 are facts which also require explanation if we are to accept these views as to the relation 

 of nerve -supply to muscle-homology. Thus the biceps and its accessory parts receives 

 twigs from (1) the pudic ; (2) the nerve to the ham-strings ; (3) the external saphenous ; 

 (4) the musculocutaneous : the adductor magnus is entirely supplied by the nerve 

 to the quadratus femoris ; and the inner head of the gastrocnemius in the discus receives 

 a twig from the external saphenous. If the souree in the spinal cord from which the 

 nerve fibres are derived is invariably the same, it is at least certain that the nerve-strands 

 through which the fibres reach the muscle are often very different. 



From the facts that I have brought forward, I think that we are entitled to conclude 

 that the doctrine of the invariable relation between nerve-supply and muscle-homology 

 is an erroneous one, and contrary to existing fact. 1 The value of this feature, however, 

 in the determination of the history of a muscle cannot be overrated. Indeed, it is 

 hardly equalled in importance by the " insertion." 



Lastly, I consider that it is not at all unlikely — indeed, that it is highly probable — 

 that the source in the brain or spinal cord from which the nerve fibres, destined for the 

 supply of a certain muscle, are derived is invariably the same. Of this, however, we 

 have little proof. It is a matter of certainty, as we have seen, that these fibres may 

 adopt different nerve-strands in order to reach the muscle. Even in the human body 

 great numbers of examples of this may be quoted. Thus the long buccal nerve has been 



1 Since the above was written, after, indeed, it was published in the form of an abstract (Relation of Nerve-Supply 

 to Muscle-Honiology, Jour. Anat. and Phys., vol. xvi.), a highly important paper by Dr. Hans Gadow has appeared, 

 enlitled " Beitrage zur Myologie der hinteren Extremitat der Keptilien " (Morpholog. Jahrbuch, 1881). It is very satis- 

 factory to find that, although a pupil of the Heidelberg school from which the doctrine of the immutability of nerve- 

 supply originally emanated, he has arrived at results very similar to my own. Working, however, at lower forms than those 

 offered by the Mammalian order he has had a better opportunity afforded him of clearing up the question. In my 

 investigations I have been led to believe that wherever a muscle possessed a double nerve-supply this pointed to the 

 amalgamation of two originally distinct muscles. Dr. Gadow, however, has proved that this interpretation only 

 applies to comparatively few cases. In mammals it is rare to meet with a muscle which draws its nerve-supply from 

 two different sources ; in Man the adductor magnus, the pectineus and brachialis anticus are the best examples of this, 

 and we have met with several other instances in the lower members of the group. In the lower animals, however, it is 

 an extremely common occurrence, and Dr. Gadow has shown that the percentage of double-nerved muscles diminishes 

 as we ascend the animal series from the Reptilia, through the birds, up to mammals ; whilst at the same time the number 

 of muscles increases. He concludes, therefore, that in the majority of cases double-nerved muscles show the original 

 state, and that these muscles afterwards may become single-nerved muscles by splitting up into two or more separate factors. 



