The terminal branches are composed of a se. ries of cutaneous branches to the back part ol the ankle, heel, and back part of the outer edge of the foot, and a long nerve, the continuation of the trunk directed along the outer edge of the foot to supply the outer margin of the little toe, communicating previously with the musculo-cutaneous.
The termination of the tibial saphmnus nerve is subject to considerable variation, both as to size and distribution. It occasionally forms no connection with the peronmal saphmnus, and then is very large. When united with the peronmal saphrenus, so as to form the ex ternal saphmnus, its terminal branch not un frequently divides into two ; the one division for the opposed edges of the fourth and fifth toe ; the other for the outer edge of the latter. We have observed the saphtenus nerve sup plying also the opposed edges of the third and fourth toes, whilst the musculo-cutaneous in this instance supplied naerely the inner edge of the great toe and the opposed margins of the second and third toes.
The tibial nerve, before dividing into the in ternal and external plantar, gives off, a little above the ankle, an internal calcaneal branch, which in a high division of the nerve comes away from the external plantar. Having sup plied the skin at the inner aspect of the heel, it winds beneath the inferior surface of the os calcis, and communicates with the calcaneous branch of the external saphtenus.
The internal plantar nerve, larger than the external and analogous to the median nerve in the hand, passes behind the internal malleolus superficial to anti distinct from the tendons of the tibialis posticus, and in front of the pos terior tibial vessels. It then runs above the abductor pollicis, and is directed in the intermuscular septum, between it and the flexor brevis digitorum. Having perforated this, it appears between the two muscles, and divides into internal and external branch es The internal branch is smaller than the ex ternal, passes froin without inwards over the tendon of the long flexor of the toe to the inner side of the metatarsal bone, gives fila ments to the abductor pollicis, flexor brevis, and the skin, and terminates at the inner side of the toe, supplying in its course filaments to the articulations, and when it reaches the last phalanx, a small cutaneous branch to the dorsum.
The external branch divides after a course of about an inch or two. The internal division, as it is directed along the first interosseous space, gives off in its course filaments to the first interosseous and lumbricalis, and at the anterior part of this space divides into two twigs for the opposed sides of the great and second toe. The external division, after a very short course, divides into two branches : the internal crosses obliquely the second in terosseous space, gives filaments to the second lumbricalis, and bifurcates at its anteriot• ex ' treniity for the supply of the opposed sides of the second and third toes : the external • crosses obliquely to the third interosseous r space, and like the preceding divides at its anterior extremity into two twigs for the opposed sides of the third and ourth toes, havIng previously communicated with the ex ternal plantar.
These different divisions of the internal plantar nerve give off, in their course, fila ments to those portions of the cuticle with which they are in relation ; and also small twigs for the metatarso-phalangeal and pha langeal articulations, and muscular branches to the flexor digitorum brevis, over the ten dons of which the different divisions of the external portion of the nerve are obliquely and superficially directed.
The external plantar nerve, smaller than the internal, is directed forwards and out wards between the musculus accessorius and flexor digitorum brevis, giving filaments to either, and, having reached the inner border of the abductor mimmi digiti, which muscle it sup plies, divides into a deep and superficial branch.
The deep branch passes from between the first and second layer of muscles to place it! self between the latter and the third, passing in company with the external plantar artery. It describes a curve, the concavity of which looks towards the heel and inner malleolns. Filaments are sent off for the two outer lum bricales, for the transversalis pedis, the ad ductor pollicis, the interossei, and the tarsal and metatarsal articulations.
The superficial branch passes obliquely for! wards and outwards between the flexor brevis diaitorum and abductor minimi digiti, to both of.which it gives filaments, and soon divides into an external and internal branch.
The external branch reaches the outer border or the foot, and terminates at the extremity of the outer aspect of the little toe; giving filaments to the flexor brevis minimi digiti and the articulations. The internal, larger, com municates with the most external division of the internal plantar, and bifurcates at the ex tremity of the fourth interosseous space, for the supply of the contiguous sides of the fourth and fifth toes. The divisions of the superficial branch of the external plantar nerve, like those of the internal, supply the portions of the integument with which they are in relation, as also the articulations over which they pass.
The internal and external plantar nerves are, in reference to size, dirdetly the reverse of the corresponding arteries : the fotmer giving off seven filaments for the supply of the three inner toes, and half of the fourth ; and being analoaous in its distribution to the median in the 1;.and : the latter giving off only three filaments for the fifth and half of the fourth toe, and corresponding with the bution of the termination of the ulnar nerve. (Nathaniel Ward.)