356 The Nerves and Muscles of the Leg 
In the development of the human embryo it has been shown that two fairly 
distinct chief myogenous regions are to be distinguished on the plantar side 
of the crus and that one of these gives rise to the gastrocnemius-soleus group, 
the other to the deeper muscles of the back of the leg. Both BHisler (1895) 
and MecMurrich have performed a distinct service in again emphasizing that 
in the vertebrate series a superficial plantar musculature of the crus is 
to be distinguished from a deep plantar musculature. In many mammals, at: 
least, including man, the two layers of musculature are separated by a fascial 
septum which passes from the fibular to the tibial side of the leg and in which 
run the main nerves and blood-vessels of the back of the crus. In the reptiles 
also there appears to be a similar fairly distinct division between the super- 
ficial and the deep plantar muscles of the crus. In them, however, tne 
muscles called plantaris superficialis tenuis and plantaris superficialis accesso- 
rius by McMurrich seem to be related proximally to the superficial muscuia- 
TABLE XXVIII. 
Urodela. Reptilia. | Marsupalia. Man. 
: t | Crural Tendon of Fascial Insertions eee SEE SIS 
Ischio Flexorius. | , = of Biceps, Semiten- 
flex. tib. ext. of Flexors of Knee. 3 me 
| dinosus and Gracilis. 
Plantaris sup. med. Gastrocnemius med.} Gastrocnemius med. 
Plantaris sup. | 
minor, (Hisler.) | | 
[Plant. prof. ITI, 
minor, Mc.M.] 
| Plantaris sup. ten- Plantaris. Plantaris. 
J uis. 
Plantaris sup. | 
major, (Hisler). 
{Plant. prof. III, 
Mc. M.j | 
|| Plantaris sup. lat. Gastrocnemius lat. Gastrocnemius lat. 
Plant. sup. lat. 
(Me. M.) J|| Plantaris sup. ac- Soleus (all but deep 
cess. portion.) 
ture while distally they are inserted into the deep musculature. The plan- 
taris superficialis tenuis lies chiefly superficial to, the plantaris superficialis 
accessorius, chiefly deeper than the nerve trunks which correspond with the 
nn. plantaris medialis and lateralis of the mammals (rr. superficiales medialis 
and lateralis of McMurrich). In the amphibia there seems to be a distinct 
division between the deeper musculature and a superficial group of muscles 
composed of the muscles called by McMurrich the plantaris superficialis 
medialis, the plantaris superficialis lateralis and the plantaris profundus I1J1. 
Comparing the conditions found during embryonic development of the human 
crus with those present in the legs of the lower mammals and inferior verte- 
brates I should prefer to rearrange McMurrich’s table as shown in Table 
XEXCVTT, 
It seems probable that the muscles into which the superficial musculature 
of the plantar surface of the crus becomes divided are not perfectly homo- 
logous in the amphibia, reptiles, and mammals, although there are some 
obvious similarities. 
