REPORT ON THE MARSTJPIALIA. 40 



f 1. Flexor brevis minimi digiti. 

 b. The short muscles of ! 2. Abductor minimi digiti. 



the little toe, ] 3. The occasional opponens minimi digiti. 



c. The interossei, 



4. The occasional abductor ossis metatarsi minimi digiti. 



1 . Four dorsal. 



2. Three plantar. 



The determination of muscle homologies. — In tracing the history of any muscle or 

 group of muscles the characters upon which most dependence is to be placed are clearly : 

 (1) the position, (2) the insertion, (3) the nerve supply. Not one of these, however, can 

 In looked upon as an infallible guide. The insertion, inasmuch as it involves the action 

 or function of a muscle more than the origin, is of considerably greater importance. The 

 origin, and in a corresponding measure, the position of a muscle are changealile features 

 upon which we cannot place much reliance. The best example which can be given of 

 this is the descent of the different bellies of the extensor brevis digitorum from the 

 fibular aspect of the leg to the dorsum of the foot. Still in the group of muscles with 

 which we have to deal instances of the same kind are by no means infrequent. Thus the 

 marginal intrinsic muscles of the foot (i.e., the abductor minimi digiti and abductor 

 hallucis) show an invariable tendency to extend backwards to the os calcis for their origin, 

 and, when the hallux or minimus is absent, the dorsal interosseus which thus becomes 

 marginal commonly exhibits a like tendency unless it be confined by a rudimentary 

 metatarsal. The adductors perhaps more than any other members of the intrinsic group 

 tend to shift their origin according to the requirements demanded of them. The character 

 of these changes will be fully discussed later on. 



Dr. Georg Ruge of Heidelberg insists strongly upon the invariable and immutable 

 relationship between nerve supply and muscle homology. He asserts with Gegenbaur 

 that a muscle is to be regarded as the end-organ of a nerve, and therefore when a muscle 

 alters in position and connections its' original and typical relations can always be identified 

 by its nerve of supply. 1 That this is a most valuable aid in our endeavours to discover 

 t he history of a muscle no one will deny ; but that it is an infallible guide is a view which 

 is contrary to fact. We shall afterwards have occasion to refer to this. 



Recognising, then, the importance of the nerve supply as a guide in the determination 

 of muscle homology, I have, in the present inquiry, examined the plantar nerves in con- 

 nection with the muscles in as many cases as it was possible to do so. 



In the human foot we find that the abductor hallucis and the flexor brevis hallucis 

 are supplied by the internal plantar nerve, whilst all the other intrinsic muscles receive 

 their nerve supply from the external plantar nerve. The second and first dorsal 

 interossei sometimes receive additional nerve fibres from the anterior tibia] nerve on the 



1 Processes in the Development of the Musrles of the Human Foot, Morphologisches Jahrbuch, 1878, p. 137. 



(ZUOL. CHALL. EXP. PART XVI. lSSl'j Q 7 



