PHYLOGENY OF THE PALZOGNATHA AND NEOGNATH®. 245 
be inserted into the shaft of the tibia, below the neck. As it passes the middle head 
of the gastrocnemius it gives off thereto, at right angles, a delicate tendinous band. 
In Rhea it is small, sharply truncated forwards, terminating distad of the ventral 
border of the accessory semitendinosus. Its antero-dorsal angle fuses with the tendon 
of the semitendinosus, distad of its accessory head. Its postero-ventral angle sends 
downwards a long slender tendon to the gastrocnemius, to be inserted a short distance 
above the tarsal joint. 
In Struthio, according to Garrod, the semimembranosus tendon fuses with that of 
the accessory semitendinosus and then passes down the leg as a long thin tendon to 
the tendon of the gastrocnemius. Thus closely resembling that of Rhea. 
The ambiens is wanting only, among the Struthiones, in Dromeus.  Casuarius, 
however, is generally regarded as wanting this muscle. 
In Struthio its origin is peculiar, being from the ilium instead of the pectinal 
process of the pubis. 
In Apterya its origin is from the pectineal process of the pubis; as usual, it is 
inserted into the flexor perforatus digiti u. It does not, according to Beddard, give. 
off slips to the other two muscles of the perforatus complex. “ Furthermore, these 
small tendinous bands, accompanied by muscle-fibres, and forming a thin, flat sheet of 
tissue, are continuous with the ambiens tendon above, and appear to be in connection 
at the other end with the short arm of the biceps sling, and to arise from the fibula. 
I look upon this sheet of muscle and tendon as a second head of the flexor in 
question, and as corresponding to the fibular head of birds, such as Nycticorax. If 
this be so, Mitchell’s contention that the ligamentous head in question is a rudimentary 
ambiens is not so certain as it seemed to be, for both occur in Apterya. I found the 
same state of affairs in A. haasti.” 
In Rhea americana, Gadow [25] found the ambiens to be typically developed. ‘This 
I am able to confirm from my own dissections. 
I would remark that in an adult of this species the ambiens tendon, at the level of 
the head of the fibula, sent upwards a tendinous slip to the fibrous tissue of the lower 
border of the tendinous insertion of the crureus and origin of the fl. perf. d. m1. and 
perf. et perf. d. 11, and a few fibres to the tendinous portion of the origin of the 
common belly of the fl. u.-1v. and perf. et perf. m1. 
In R. macrorhyncha he found that “ the muscle arose from the latero-dorsal aspect 
of the pubic spine, and at the same time from the big crural vein, the muscular and 
aponeurotic fibres of the muscle having firmly got hold of the ventral aspect of this 
vein. .... The tendon of the muscle passed the knee in the typical way. 
“In R. darwini, 2, the m. ambiens of either side arose frem the pubic spine as 
usual, but its tendon, before reaching the knee, became flattened out and attached 
itself with a broad fan-shaped and very thin aponeurosis to the patella, in a similar 
style as the median additional portion of the m. femoro-tibialis (m. vastus).” Ina 
vou. xv.—Parr v. No. 18.—December, 1900. 2M 
