J. Playfair MeMurrich 435 
homologies of the human plantar muscles, and the final determina- 
tion of some of them requires more extensive material than has been 
at my disposal. But one point is, I believe, conclusively settled, and 
that is the arrangement of the human plantar muscles in a series of 
layers which are homologous with those found in both the reptila and 
the amphibia. This point established gives a broader basis for com- 
parison than the study of individual muscles can afford, and, it is to 
be hoped, will lead to a full understanding of the morphology of the 
plantar muscles. The identifications described above may be repre- 
sented in tabular form as follows: 
Lacertilia. Man. 
Flexor brevis digitorum. 
Flexor brevis superficialis str. super- | Medial head of flexor brevis hallucis. 
ficiale. Abductor hallucis. 
Abductor quinti digiti. 
Flexor brevis superficialis str. pro- (Portion of slip of flexor brevis digi- 
fundum. torum to 3d digit. 
Lateral head of flexor brevis hallucis. 
Flexor brevis medius str. superficiale. { Traribeicalon: 
Adductor hallucis. 
Flexor brevis medius str. profundum. { Opponens hallucis? 
Flexor brevis quinti digiti. 
Opponens quinti digiti. 
Interossei. 
Flexor brevis profundus. 
Intermetatarsales. 
SUMMARY. 
1. The plantar muscles in the urodele amphibia are arranged in four 
layers and are all intrinsic to the foot, arising either from the plantar 
aponeurosis or from the bones of the foot. 
2. In the lacertilia the number of layers becomes increased to six by 
the division of the superficial and middle layers so that in each of them 
there is a stratum superficiale and a stratum profundum. 
3. The plantar aponeurosis has also differentiated into two layers, 
the deeper of which forms the plantar portion of the tendons of the 
long flexors. 
4. In the mammalia the six layers found in the lacertilia persist. 
5. The marginal portions of the flexor brevis superficialis early sep- 
arate from the main mass of the muscle and form the abductors of the 
hallux and minimus. 
