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



tendon. It springs from the fibrous structures on the deep surface of the middle 

 cuneiform bone, and is inserted upon the outer aspect of the base of the first phalanx of 

 the hallux. The adductor annularis is present in the form of a distinct fibrous band 

 which rises from the tarsus beside the preceding, and is inserted upon the inner aspect of 

 the base of the first phalanx of the annular digit. It contains no muscular fibres. Its 

 position and connections alone tell its history. 



Intermediate layer. — The three middle digits (i.e. index, medius, and annularis) are 

 each provided with a well-marked and two-headed flexor brevis, which exhibits the usual 

 connections. An aponeurotic band occupies the place of the inner head of the flexor brevis 

 hallucis, whilst the outer head of the flexor brevis minimi digiti is represented by a slender 

 fibrous cord. In the former a few fleshy fibres may be detected close to its origin. 



Dorsal layer. — In this group we find — 



1. An abductor hallucis. 2. Two dorsal interossei. 



3. An abductor minimi digiti. 



The abductor hallucis is a well-developed muscle which arises from the inner and 

 under surface of the internal cuneiform bone, and is inserted into the inner sesamoid at 

 the base of the hallux. 



The first and second dorsal interossei are also well marked and present the usual 

 insertions (viz., into the inner side of the base of the index and the outer side of the base 

 of the medius respectively). They are single-headed muscles, and quite distinct from the 

 flexores breves of these digits although closely applied to them. 



A strong fibrous cord connects the shaft of the second metatarsal bone with the inner 

 sesamoid of the medius. This may represent the second dorsal interosseus. Again, a 

 strand of tough connective tissue which is attached by one extremity to the plantar 

 aspect of the base of the fourth metatarsal bone and by the other to the outer sesamoid 

 of the annularis may represent the fourth dorsal interosseus. 



The abductor minimi digiti is a very feeble muscle. 



Nervous arrangements. — In the foot of the Beaver there is very marked departure 

 from the ordinary and typical distribution of nerves to the intrinsic muscles. 



The internal plantar nerve divides into the usual four digital branches viz., (1), for the 

 inner side of hallux, (2) for the adjacent sides of hallux and index, (3) for the adjoining- 

 sides of the index and medius, and (4) for the contiguous margins of the medius and 

 annularis. From these, three muscular branches proceed for the supply of the intrinsic 

 muscles. The first comes from the digital nerve to the inner side of the hallux and 

 supplies the abductor hallucis. The second is the largest of the three, and takes origin 

 from the third digital nerve. It sinks into the sole in the interval between the Ions; 

 flexor tendons which go to the index and medius, and breaks up into twigs which sj)read 

 out to supply the adductor hallucis, the first dorsal interosseus, the flexor brevis indicis, 



