414 The Phylogeny of the Plantar Musculature 
and by the fact that it is supplied by a branch given off from the lateral 
plantar nerve before it bends dorsally to reach its final position between 
the middle and deep layers of flexors. 
The stratum profundum (Fig. 4, fbsp) of the flexor superficialis is 
represented by two muscles which take their origin from the plantar sur- 
face of the tendon of the plantaris profundus II-III before it separates 
into its terminal slips. The muscle lies in the intervals between the second 
and third and third and fourth of these terminal slips, and some of their 
fibers arise from the slips passing to the third and fourth digits. The 
more tibial muscle is directed fibularly in its distal course, and, passing 
over into a tendon, is inserted into the tibial side of the base of the proxi- 
mal phalanx of the third digit, in close proximity to the slip of the flexor 
brevis medius str. superficiale to that digit. The more fibular muscle has 
almost the same relations, except that it fuses with the large slip of the 
flexor brevis medius str. superficiale to the fourth digit, forming a mus- 
cular mass which completely invests the plantaris profundus III-IT ten- 
don to the digit. The relations of the muscles are practically identical in 
both Scincus and Iguana; they seem to correspond to the muscles 7 and € 
of Gadow’s, 82, second layer and to those numbered 17 and 18 by Perrin, 
93. 
The flexor brevis medius is represented by two distinct muscle layers. 
The stratum superficiale (Figs. 3 and 4, foms), lies immediately dorsal to 
the tendons of the plantaris profundus III-IT, and in Scincus consists at 
its origin of three portions. The tibial and middle portions arise from 
the plantar surface of the base of the second and fourth metatarsals and 
from the connective tissue covering those bones, while the fibular portion, 
much the strongest of the three, has an extensive origin from the fibular 
border of the fifth metatarsal. The tibial and fibular portions retain their 
individuality throughout, the former passing distally and tibially to be 
inserted into the first metatarso-phalangeal fibro-cartilage, while the latter 
passes to the corresponding structure of the fourth digit. The middle 
portion divides into two slips, which pass respectively to the metatarso- 
phalangeal fibro-cartilages of the second and third digits (Fig. 4, 
Usa ae 
In Iguana the arrangement of the layer is essentially the same as in 
Scincus, although there are some differences in detail. The muscles 
take origin in part from the tarsal bones, instead of from the meta- 
tarsals, and in part receive numerous fibers from the dorsal surfaces of 
the tendons of the plantaris profundus III-II. The tibial portion is 
strong and quite independent of the others; the median portion, which 
