368 The Nerves and Muscles of the Leg 
Comparative anatomy of the intrinsic plantar muscles.—According to Mc- 
Murrich, 04, the muscles of the crus terminate primarily at the ankle either 
on the plantar aponeurosis or the tarsus. The tendons whereby the long 
flexors of the toes are attached to the digits he looks upon as a differentiation 
of a deep plantar aponeurosis. According to this view the foot, in which 
but one set of crural muscles is attached through tendons to the digits, is to 
be looked upon as more primitive than the hand, in which superficial and deep 
forearm flexors are thus attached. In the foot there are to be distinguished 
several layers of intrinsic muscles, the more superficial of which, the 
flexor digitorum brevis and the lumbricales, arise in man from or in con- 
nection with the plantar aponeurosis or its derivatives, while the deeper lay- 
ers arise from the tarsus and metatarsus. 
The deeper intrinsic muscles of the hand and foot are considered by Cun- 
ningham, 82, and Brooks, 87, to have been derived from three primary 
layers, a superficial layer of four muscles primarily adductors, an interme- 
diate layer of bicipital short flexors, one for each digit, and a deep layer of 
six abductors. The lateral plantar nerve crosses between the superficial and 
the intermediate layer.” 
MeMurrich, 03, differs greatly from Cunningham in the layers to which 
he would ascribe the muscles of the hand. Thus he recognizes the following 
layers: 
Flexor brevis superficialis: Palmaris brevis, abductor digiti quinti, oppo- 
nens digiti quinti, flexor brevis digiti quinti, abductor pollicis, opponens pol- 
licis, flexor pollicis brevis. 
Flexor brevis medius, stratum superficiale: The lumbricales. 
Flexor brevis medius, stratum profundum: The adductor pollicis. 
Flexor brevis profundus: The interossei volares, interossei dorsales (in 
part). 
Intermetacarpals: The interossei dorsales (in part). 
McMurrich has not yet published his paper on the phylogeny of the muscles 
of the foot, so that his views as to the origin of these muscles cannot be 
given, but doubtless the layers there, from his point of view, resemble those 
of the hand. 
The subject of the comparative anatomy of the plantar muscles is too intri- 
cate to be entered upon here at length. Leche gives a brief summary of the 
conditions found in the mammalian series. 
From the standpoint of embryological development the division of the deep 
plantar muscles adopted by Ruge, 78, is of the greatest value. He recog- 
nizes a medial group consisting of the abductor and the flexor brevis hallucis, 
innervated by the medial plantar nerve, and two groups innervated by the 
lateral plantar nerve, a more superficial group of ‘“ contrahentes ’”’ which lie 
plantarwards from the deep branch of the nerve and a group of “ interossei ”’ 
which lie deeper than this nerve. He also points out that in many of the 
mammals the interossei have permanently a plantar position which corre- 
sponds with the early embryonic condition in man. 
* See Quain’s Anatomy 10th ed., Vol. II, Pt. II, p. 276. 
