314 The Nerves and Muscles of the Leg 
adductor magnus in most mammals is innervated merely by the obturator 
nerve and there is a special presemimembranosus muscle (W. Leche) which 
extends usually from the tuber ischii to the medial side of the distal end of 
the femur parallel with the semimembranosus. In the gorilla, orang, and 
gibbon the presemimembranosus is combined with the adductor magnus, as 
it is in man (‘W. Leche). In many forms the presemimembranosus is more 
or less fused with the semimembranosus. It may be looked upon as derived 
phylogenetically from the semimembranosus or medial flexor of the thigh 
(A. Biihler, 03). In echidna the adductor magnus is innervated both by 
the obturator and sciatic nerves (W. Leche). 
In urodeles the elements of the adductor group are probably contained in 
the pubi-ischio-femoralis externus and possibly also in part in the pubi- 
ischio-femoralis internus. The pubi-tibialis may represent the mammalian 
presemimembranosus and the sciatic portion of the adductor magnus in man. 
In reptiles the adductor elements are contained in the pubi-ischio-femoralis 
externus (and the ischio-femoralis, Gadow). In the different groups of mam- 
mals there is considerable variation in the number of individual muscles into 
which the adductor musculature is divisible; from one to six according to 
Le Double (97). In man the chief variations noted have to do with the 
greater or less fusion of the different muscles into which the group is 
divided. The adductor magnus may be united by fasciculi or fused not only 
with the neighboring long adductor but also, owing to the origin of its 
posterior portion from the hamstring group, with the semimembranosus 
muscle. The adductor minimus portion of the adductor magnus is frequently 
fused with the quadratus femoris and may be supplied by the same nerve 
although this portion of the muscle belongs normally chiefly to the territory 
of the obturator nerve. The short adductor is frequently fused with the 
obturator externus. 
b. Nerve Variation in the Adult. 
1. Variation in the Origin of the Obturator Nerve. 
In the great majority of instances the obturator, lke the femoral, 
nerve arises chiefly from the 22d, 23d, and 24th spinal (2d, 3d, and 4th 
lumbar) nerves. ‘Table XVI indicates the spinal roots from which the 
nerve arose in 246 instances and the various types of lumbo-sacral plexus 
with which the various modes of origin were associated. 
2. Relations of the Nerves Springing from the Obturator Nerve to the 
Spinal Nerves. 
In the case of the obturator nerve it is even more difficult than in case 
of the femoral nerve to trace with accuracy the relations of the nerves 
of distribution to the nerve roots. Examination of several nerves leads 
me to the belief that the bulk of the nerve fibres distributed to each of 
the nerves of distribution occupy in the obturator nerve as it approaches 
