PHYLOGENY OE THE PALjEOGNATEUE AND NEOGNATH^E. 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 Dromceus. 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 Apteryx its origin is from the pectineal process of the pubis; as usual, it is 

 inserted into the flexor perforatus digiti n. 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 Apteryx. 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. in. and 

 perf. et perf. d. 11., and a few fibres to the tendinous portion of the origin of the 

 common belly of the fl. ii.-iv. and perf. et perf. in. 



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 

 ve in The tendon of the muscle passed the knee in the typical way. 



" In R. darwini, $ , the m. ambiens of either side arose from 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 (in. vastus)." In a 



vol. xv. — part v. No. 18. — December., 1900. 2 11 



