12-1 



THE VOYAGE OF H.M..S. CHALLENGER. 



Plantar Layer — Adductores! (Table A) — continued. 

 Tetradact ylous Feet. 



(Hallux absent, or very rudimentary.) 



Tridactylous Feet. 



This table brings out that the plantar layer constitutes a very constant part of the 

 intrinsic muscle apparatus of the mammalian foot. In the feet of forty-six different 

 species possessed of three or more toes it is absent 'entirely in three 'cases only. In the 

 monodactylous and didactylous feet of Solipeds and Ruminants not a trace of adducting 

 muscles is to be found. But, further, the table shows the relative constancy of the different 

 members of the group. The starting-point is the Echidna, in which there are five muscles, 

 one for each toe. Ruge 1 considers the original number to be six, and he describes that 

 number in the Ornithorhynclius, viz., two for the minimus, and one for each of the other 

 digits. One of the two which he refers to the minimus we have already seen to be in 

 reality the outermost belly of the flexor brevis digitorum, and not an intrinsic muscle at 

 all. Although I was unable to find an adductor indicis in the. four specimens of this 

 animal I examined, I would consider that its occasional presence is a very likely occurrence 

 seeing that it is constantly present in the Echidna. A glance at the table will show that 



1 Upon the Comparative Anatomy of the Deep Muscles of the Sole of the Foot. 



