1884.] MR. G. E. DOBSON ON THE HALHTX OF MAMMALS. -403 



shcJ, and a young female, a few montlis old, in which these teeth 

 are well developed, although the canines have but partially descended. 

 The adult female differs from other adult specimens of E. albiventris 

 in possessing, in the left hind foot, a minute hallux represented 

 (external to the integument) by the presence of its claw only, 

 although in the right hind foot there is no trace of this digit ex- 

 ternnlly. On the other hand, in the young female above referred 

 to, both hind feet possess a minute hallux, which, on dissection, I 

 find consists of the usual number of phalanges, and, although there 

 appears to he no trace remaining of flexores breves muscles, yet 

 there is a distinct flexor tendon given off to the terminal phalanx by 

 the flexor digitorum fifjularis {flexor hallucis lonffus), and an extensor 

 by the extensor hallucis Ioik/us. 



On carefully rc-flecting the integument from the sole of the right 

 foot of the adult female, I find that, while the tendons of these 

 muscles are still represented, the phalanges of the hallux have quite 

 disappeared, the metatarsal bone alone remaining, having its distal 

 extremity connected with the under surface of the iiitegument by 

 hgamentous structures only, to which the tendon of the extensor 

 hallucis longus is still attached on one side, and the very rudimentary, 

 fascia-like slip, representing the remains of the tendon from the 

 flexor digitorum fihularis {flexor hallucis longusY, on the other. 



Here, then, we have a digit which appears to have undergone 

 degeneration during the life of the animal, for it is reasonable to 

 suppose that this female when young was provided with a hallux in 

 each hind foot, like the young one in the same collection, and, as 

 we find complete absence of this digit in both hind feet of other 

 specimens of this species", we are led to believe that either they 

 possessed halluces when young and subsequently lost them, or that 

 we have in the specimens above described examples of a local variety^ 

 of the same species in which these digits are still persistent, though 

 in a very rudimentary state, and that the loss of that describ?d was 

 due to some accident. In either case, however, we have here an 

 interesting demonstration of the progressive disappearance of the 

 hallux within a single genus. 



' For explanation of the use of these terms for the long flexor nniscle of the 

 foot in Erwacens, see my paper " On the Homologies of the Long Flexor 

 Muscles of the Feet of Mammalia " in Journ. Anat. Phys. vol. xvii. jip. 14G- 1-18. 



^ The hallux is altogether wanting, as determined by me by dissertion; there 

 is not even a trace of the metacarpal bone of this digit remaining in either of 

 the hind feet of the specimens examined. 



^ It is interesting to note that, in these two Lagos specimens of E. albivenfris, 

 a small black streak is found on the wkite fur of the face between the eyes and 

 on each cheek, representing the large similarly placed patches of dark-ccloured 

 fur on the face of E. diadcmafus as the rudimentary halluces represent the 

 much more developed yet very small corresponding digits of that species, which, 

 probably, still closely resembles the ancestral form from which both .species 

 were derived. 



