on the Conformation of Bones 385 



muscles of the whole adductor group will be those attached in the 

 region of the knee; so also in flexed positions of the knee. It is 

 thus that the perpendicular from muscle to joint is the longest — 

 and this is a measure of the leverage. The femur is of course prac- 

 tically always longer than the postacetabular pelvis ; if shorter, the 

 muscle would have to be placed at right angles to the femur for 

 optimum leverage effect. 



In more extended positions of the thigh (Fig. 5) such "adductor" 

 muscles as pass to the knee-joint will be at some disadvantage; 

 the most effective muscles will now be attached further up the 

 shaft; and the greater the extension, the higher up the shaft will 

 hip extensors be required. 



A relatively longer femur will after a smaller movement of ex- 

 tension involve the employment of these shaft "adductors," 

 rather than those of the knee. AppUcation of these principles to 

 the cursorial, saltatorial, and arboreal animals shows some corre- 

 ^ spondence with actual hfe. 



Arboreal animals require a greater range of extension at the 

 hip than do cursorials; and the mass of their adductors is attached 

 to the femoral shaft (Fig. 5). Ungulata present a much smaller 

 range of extension (Fig. 4 c). Carnivora are intermediate and so 

 is their adductor musculature {vide Table I). 



Again, cursorials present a shortened femur, not only as com- 

 pared with other limb-segments (Gregory), but as compared with 

 the postacetabular pelvis (Fig. 4 c, cow). This will in itself involve 

 the continued use of the semimembranosus at a range of exten- 

 sion at which in longer-hmbed animals shaft adductors might be 

 employed. Hence the concentration of "adductors" at the knee in 

 Artiodactyla and other cursorials and jumpers; and, along with this, 

 changes in the form of the femur. 



That shortening of the femur, alone, will not result in the cur- 

 sorial pattern of adductors, viz. with attachment largely to the 

 knee-region, is shown in the gorilla (Fig. 5); in him, a large part 

 of the adductors is attached to the middle of the shaft, in associa- 

 tion with the habitual employment of the thigh in the almost fully- 

 extended position. In man, the ratio of shaft to knee adductors is 

 large also, larger than the figure in Table I would suggest; his 

 semimembranosus is in fact reduced far below its size in the gorilla ; 

 extension from full flexion is not a frequent or habitual movement. 



The conditions governing adductor attachment, in so far as 

 true adduction is concerned, are probably similar; in man the 

 extensor function of the group is largely taken over by the en- 

 larged gluteus maximus {sen superficiahs) owing to the unsatisfactory 

 position of the adductors; and the adductor longus in particular 

 has become an adductor ixir excellence. The relationship of the 

 form of the preacetabular part of the pelvis to the functions of the 



