SURFACE FORM OF THE LOWER EXTREMITY. 449 



the other muscles in the sole of the foot by the external plantar. The first dorsal 

 interosseous muscle frequently receives an extra filament from the internal branch 

 of the anterior tibial nerve on the dorsum of the foot, and the second dorsal 

 interosseous a twig from the external branch of the same nerve. 



Actions. All the muscles of the foot act upon the toes, and for purposes of 

 description as regards their action may be grouped as Abductors, Adductors, 

 Flexors, or Extensors. The Abductors are the Dorsal interossei, the Abductor 

 hallucis, and the Abductor minimi digiti. The Dorsal interossei are abductors 

 from an imaginary line passing through the axis of the second toe, so that the 

 first muscle draws the second toe inward, toward the great toe ; the second 

 muscle draws the same toe, outward ; the third draws the third toe, and the 

 fourth draws the fourth toe, in the same direction. Like the interossei in the 

 hand, they also flex the proximal phalanges and extend the two terminal pha- 

 langes. The Abductor hallucis abducts the great toe from the others, and also 

 flexes the proximal phalanx of this toe. And in the same way the action of the 

 Abductor minimi digiti is twofold as an abductor of this toe from the others, 

 and also as a flexor of the proximal phalanx. The Adductors are the Plantar 

 interossei, the Adductor obliquus hallucis, and the Adductor transversus hallucis. 

 The plantar interosseous muscles adduct the third, fourth, and fifth toes toward 

 the imaginary line passing through the second toe, and by means of their inser- 

 tion into the aponeurosis of the extensor tendon they flex the proximal phalanges 

 and extend the two terminal phalanges. The Adductor obliquus hallucis is 

 chiefly concerned in adducting the great toe toward the second one, but also 

 assists in flexing this toe. The Adductor transversus hallucis approximates all 

 the toes, and thus increases the curve of the transverse arch of the metatarsus. 

 The Flexors are the Flexor brevis digitorum, the Flexor accessorius, the Flexor 

 brevis hallucis, the Flexor brevis minimi digiti, and the Lumbricales. The 

 Flexor brevis digitorum flexes the second phalanges upon the first, and, con- 

 tinuing its action, may flex the first phalanges also and bring the toes together. 

 The Flexor accessorius assists the Long flexor of the toes, and converts the 

 oblique pull of the tendons of that muscle into a direct backward pull upon the 

 toes. The Flexor brevis minimi digiti flexes the little toe and draws its meta- 

 tarsal bone downward and inward. The Lumbricales, like the corresponding 

 muscles in the hand, assist in flexing the proximal phalanx, and by their inser- 

 tion into the long Extensor tendon aid in straightening the two terminal pha- 

 langes. The only muscle in the Extensor group is the Extensor brevis digi- 

 torum. It extends the first phalanx of the great toe, and assists the long Exten- 

 sor in extending the next three toes, and at the same time gives to the toes an 

 outward direction when they are extended. 



Surface Form. Of the muscles of the thigh, those of the iliac region have no influence 

 on surface form, while those of the anterior femoral region, being to a great extent superficial, 

 largely contribute to the surface form of this part of the body. The Tensor fasciae, femoris 

 produces a broad elevation immediately below the anterior portion of the crest of the ilium and 

 behind the anterior superior spinous process. From its lower border a longitudinal groove, 

 corresponding to the ilio-tibial band, may be seen running down the outer side of the thigh to 

 the outer side of the knee-joint. The Sartorius muscle, when it is brought into action by 

 flexing the leg on the thigh and the thigh on the pelvis, and rotating the thigh outward, 

 presents a well-marked surface form. At its upper part, where it constitutes the outer 

 boundary of Scarpa's triangle, it forms a prominent oblique ridge, which becomes changed into 

 a flattened plane below, and this gradually merges in a general fulness on the inner side of the 

 knee-joint. When the Sartorius is not in action, a depression exists between the Extensor 

 quadriceps and the Adductor muscles, running obliquely downward and inward from the apex 

 of Scarpa's triangle to the inner side of the knee, which corresponds to this muscle. In the 

 depressed angle formed by the divergence of the Sartorius and Tensor fasciae femoris muscles, 

 just below the anterior superior spinous process of the ilium, the Rectus femoris muscle appears, 

 and, below this, determines to a great extent the convex form of the front of the thigh. 

 In a well-developed subject the borders of the muscle, when in action, are clearly to be defined. 

 The Vastly externus forms a long flattened plane on the outer side of the thigh, traversed by 

 the longitudinal groove formed by the ilio-tibial band. The Vastus interims, on the inner side 

 of the lower half of the thigh, gives rise to a considerable prominence, which increases toward 

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