a. Cut through the Internal Plantar nerve behind, and throw it over the toes. The branches of the artery of the same name, to the second, third, and fourth interosseous spaces, must be divided if present.
b. Divide the Plexor brevis digitorum muscle, and throw it towards the toes. Its nerve from the Internal Plantar will be torn through. There will now be exposed—
1. The tendon of the Plexor longus digitorum muscle.
This is seen to be dividing into four slips, one for each of the four outer toes. They each enter the corresponding Digital sheath beneath the Flexor brevis tendon. The following are also seen connected with this muscle, viz.— a. The Accessorius muscle, passing from the Os Galois to the hinder border of the tendon of the Flexor longus digitorum, but from which tendinous slips are traceable to those tendons of the long Flexor which run to the second, third, and fourth toes (Turner). A portion of the Inferior Calcaneo-cuboid or Long Plantar ligament is seen behind close to the Os Galois, between its two heads of origin. 6. The Lumbricales muscles. The innermost arising from the Tibial side of the innermost tendon, the other three from the contiguous sides of the first and second, second and third, and third and fourth tendons.
2. The tendon of the Flexor longus pollicis muscle, lying beneath (in this position) the Flexor longus digitorum muscle. A tendinous slip passes from the former to the latter at the hinder part of the foot, and is said to be traceable to the slips of the Flexor longus digitorum, running to the second and third toes (Turner).
3. A further portion of the Flexor brevis pollicis muscle, running to each side of the base of the first Phalanx of the great toe, with the tendon of the Flexor longus pollicis lying between these two heads.
4. The Flexor brevis minimi digiti muscle, lying upon the Metatarsal bone of the little toe.
5. The Plantar and Dorsal Interossei muscles of the fourth space, the former lying externally.
6. The External Plantar artery, with its accompanying vein, The vessel is seen behind, emerging from beneath the Abductor pollicis muscle, and running obliquely forwards and outwards over the Acces-sorius muscle to a point opposite the base of the fifth Metatarsal bone. It then turns transversely inwards, and passes beneath the tendon of the Flexor longus digitorum muscle ; just as it makes this bend it gives off the branch to the outer side of the little toe, which has been previously seen.
7. The External Plantar nerve, taking the same course as the artery as far as the base of the fifth Metatarsal bone. At that point it is divided into a Superficial and a Deep branch. The former has been already seen dividing into two Digital branches for the little, and the opposed side of the fourth toe; besides this, the outermost of the two is now seen to be supplying the Flexor brevis minimi digiti muscle, and often the Interossei muscles of the fourth space; the inner has been found to communicate with the fourth Digital branch of the Internal Plantar nerve. The Deep division passes, with the External Plantar artery, beneath the tendons of the Flexor longus digitorum. The trunk of the External Plantar nerve may be now found supplying branches to the Accessorius and Abductor minimi digiti muscles, in the posterior part of its course which was previously covered by the Flexor brevis digitorum.
a. Divide the tendon of the Plexor longus digitorum and the Accessorius muscle transversely at their junction. This point is taken in order to leave the Accessorius muscle with the External Plantar vessels and nerve lying upon it. The tendons of the long Flexor muscle, with the attached Lumbricales, should now be reflected over the toes. As this is done two slender nerves to the two outermost Lumbricales will be found coming from the Deep branch of the External Plantar nerve. There will now be exposed—
1. The Flexor brevis pollicis muscle, most internally.
2. The Adductor pollicis muscle, external to this parallel with its outer border.
3. The Flexor brevis minimi digiti muscle, lying upon the fifth Metatarsal bone.
4. The Transversalis pedis muscle, lying transversely across the Metatarso-phalangeal articulations.
5. The Plantar and Dorsal Interossei muscles, of the , third and fourth spaces, and just the anterior end of the Plantar of the second, lying in the triangular interval formed by the Adductor pollicis, Flexor brevis minimi digiti, and Transversalis pedis muscles. The Adductor pollicis may, however, conceal the Interossei of the second space completely.
6, Further portions of the External Plantar vessels.
The portion of the artery which extends beyond the base of the fifth Metatarsal bone is called the Plantar arch. The Digital branches of the arch which run forwards in the fourth and third spaces, and the anterior part of the one in the second space, will be seen. They pass in front beneath the Transversalis pedis muscle. The Posterior Perforating offsets of the two outer Digital branches, which pass through the heads of the Dorsal Interossei to the Interosseous arteries of the Dorsum may be traced, but only the anterior part of the Digital branch of the second space will be seen, as the posterior part is concealed by the Adductor pollicis muscle. Each of these Digital branches is seen to bifurcate at the cleft of the toes, and from the point of bifurcation other slender offsets (Anterior Perforating) also to the Dorsal Interosseous arteries, are traceable.
7. The Deep branch of the External Plantar nerve may be followed to its ending in the Adductor pollicis muscle. Branches are traceable to the Transversalis pedis, and at this stage only to the Interossei of the third space, and the fourth when not supplied by the Superficial division. The offsets to the two outer Lumbricales have been already seen.
a. Remove now the Adductor pollicis muscle and the outer portion of the Flexor brevis pollicis muscle.
The nerves to the former from the Deep division of the External Plantar will be divided.
There will now be exposed—
1. The Interossei muscles of the first and second spaces.
2. The remaining portion of the Plantar arch and its junction at the back of the first interosseous space, with the communicating branch from the Dorsalis Pedis artery. The Digital branch of the second space is now displayed, and its Posterior Perforating offset is now traceable.
3. The arteria Magna Pollicis is seen arising from the Dorsalis Pedis artery, where it dips into the sole of the foot. This divides into two branches, the outer of which runs forwards in the first space, and bifurcates for the contiguous sides of the great toe and the next, and the inner of which passes beneath the tendon of the Flexor longus pollicis and innermost head of the Flexor brevis pollicis, to the inner side of the great toe.
4. The nerves to the Interossei muscles of the first and second spaces are now traceable from the Deep division of the External Plantar nerve. The Plantar arch is now fully exposed. If the whole of the External Plantar artery is to be uncovered, it will be necessary to remove the posterior part of the Abductor pollicis muscle and the lower portion of the Internal Annular ligament.