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



Dorsal and intermediate layers (PI. VIII. fig. 8, f 2 to/ 5 and d 2 to c/ 6 ). — It is in the 

 dorsal and intermediate layers that we find the greatest deviation from our type. The 

 flexores breves (f 2 to/ 2 ), and the dorsal interossei have undergone a partial or complete 

 amalgamation ; still there are usually traces left of a character sufficiently patent to enable 

 the dissector to determine the complex character of the muscles with which he has to deal. 

 As a rule, the fusion is complete towards the middle of the metatarsal bone, whilst 

 towards the origin and insertion a partial separation can be effected. But even in cases 

 where no true and natural separation can be made out, a close examination will usually 

 show tendinous intersections running through the muscles, and these afford a clue to their 

 composite character. 



The mode of insertion cannot be regarded as giving a sure means by which these fused 

 muscles can be distinguished from each other. The dorsal interossei, it is true, are almost 

 invariably inserted into the extensor tendon ; but, on the other hand, the flexores breves 

 are not in all cases inserted into the sesamoid bones alone. One of the two slips is 

 frequently inserted into the extensor tendon as well. 



The fused flexores breves and dorsal interossei constitute a series of muscles which are 

 frecmently described as bicipital, whilst in reality they are tricipital, and, in the case of the 

 medius, quadricipital. 



The dorsal interossei are disposed so as to abduct the toes from a line drawn through 

 the medius. In no case do they arise from the shafts of the metatarsal bones. 



It is interesting to note the different dispositions of the abducting apparatus of the 

 little toe in these animals. A tendency is exhibited to its disappearance by fusion with 

 the outer head of the flexor brevis minimi digiti. 



In the Leopard it is the most strongly developed. Here we find (1) a well-marked 

 abductor ossis metatarsi minimi digiti (fig. 8, a.o), (2) an abductor minimi digiti (d 6 ), and 

 (3) a small slip which seems to belong to this apparatus. The abductor of the metatarsal 

 bone, and the abductor of the little toe, have a common origin from the proximal and outer 

 aspect of the os calcis. Separating from each other, the former is inserted into the pro- 

 jecting base of the fifth metatarsal bone, whilst the latter is inserted by a long narrow 

 tendon upon the outer face of the base of the first phalanx of the minimus. The small 

 fleshy slip referred to above springs from the base of the fifth metatarsal, at a higher level 

 than the flexor brevis of the little toe, and after a short independent course it fuses with 

 the outer head of that muscle. Is this not the third abductor of the minimus which we 

 have seen present in some of the Marsupials ? Against this view, however, is the fact 

 that the tendon of the abductor minimi digiti is inserted both into the sesamoid bone, and 

 into the extensor tendon, on the dorsum of the first phalanx. 



In the Puma the arrangement is similar in every respect, except that no trace of the 

 third small supernumerary slip can be detected, and that the slender tendon of the 

 abductor minimi digiti is inserted into the extensor tendon alone. 



