REPORT ON THE MARSUPIALIA. Ill 



ergus and Cape Mouse the Crested Agonti and the Guinea Pig, in both of which flexores 

 breves are alone developed. 



Cheiroptera. 



Pteropus (Fox-bat), (PI. XL figs. 1 and 2). 



The foot of the Fox-bat is pentadactylous — -the four outer toes being of nearly equal 

 length, and the hallux slightly smaller. All the digits are armed with sharp curved claws. 

 The intrinsic muscles are well marked, but the dorsal or abducting members of the group, 

 with one exception, are absent. They are all placed upon the plantar aspect of the 

 metatarsus, and are all but invisible from the dorsal aspect of the foot. 



Plantar layer. — Only two muscles of this layer are represented, viz.: — 



1. Adductor hallucis (p 1 ). 



2. Adductor minimi digiti (p 5 ). 



These muscles together form a thin triangular sheet of muscular fibres spread 

 out upon the flexores breves, but separated from them by the deep division of the external 

 plantar nerve (d.d). This muscular sheet arises by its apex from the plantar surface 

 of the tarsus somewhat nearer the inner than the outer margin of the foot, and it 

 is mapped out into the two adducting muscles by a distinct fibrous raphe which extends 

 from the apex to the base. The distal end of the raphe is not attached, and ends 

 close to the inner side of the root of the meclius. The adductor minimi digiti is much 

 the larger of the two muscles, and is inserted into the inner sesamoid at the base of the 

 first phalanx of the minimus. The adductor hallucis, small in proportion to the preceding, 

 is inserted into the outer sesamoid at the base of the first phalanx of the hallux. 



Intermediate layer. — This layer is typically complete (f 1 to f 5 ). A flexor brevis is 

 provided for each digit ; each muscle consists of two heads, and these are separate 

 throughout their entire length. This group therefore is composed of eight distinct 

 muscular slips, all of which lie upon the same plane. They arise from the fibrous 

 textures at the base of the metatarsus and are inserted into the sesamoid bones alone. 



The outer head of the flexor brevis minimi digiti, and the inner head of the flexor 

 brevis hallucis, are considerably larger than the others. This increase in bulk may 

 be due to their having coalesced with the absent abductor minimi digiti, and abductor 

 hallucis. 



Dorsal layer. — The only member of this layer which is present is the abductor ossis 

 metatarsi minimi digiti (dP). It is well developed, and has the usual connections. 

 Not a trace of the dorsal interossei is to be found. 



Nervous arrangements. — The posterior tibial nerve divides into its two terminal 

 branches in the hollow of the os calcis. 



