1885.] DR. H. GADOW ON THE SPECIES OF RHEA. 317 



is remarkable for the still greater length of its toes. The propor- 

 tional shortness of the toes of the Common Rhea has already been 

 observed by Mr. Cunningham. Mr. Sclater's original statement that 

 the toes -are much shorter in his Rh. macrorhyncha than in the 

 Common Rhea cannot be confirmed. 



The proportions of the femur and tarso- metatarsus to each other 

 permit of no safe conclusions, nor do the dimensions of the pelvis, 

 owing to the considerable alterations undergone by these parts during 

 the individual growth. 



The scapula of Rh. americana seems to be much longer than that 

 of Rh. darwini, in comparison with the coracoid, although the 

 latter bone in Darwin's Rhea is absolutely stronger. This apparent 

 shortness of the scapula, however, is partly produced by this bone 

 being curved at a sharper angle in Rh. darwini. 



Muscles. 



The examination of the muscles of two Rh. americana, two Rh. 

 darwini, and one Rh. macrorhyncha did not yield many interesting 

 variations except for that most variable of all the thigh-muscles, to 

 wit the famous m. ambiens. 



In the Common Rhea this muscle was typically developed, arising 

 from the pubic spine, and its slender tendon passing the knee to 

 form one of the heads of m. flexor perforatus. In Rh. macrorhyncha 

 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 right and left side were alike ; the 

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



Rhea 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 (m. vastus). 



Rh. darwini, J, left thigh. The m. ambiens stopped at the knee 

 as in Rh. darwini 5 . 



Right thigh. — Muscle typically developed and passing the knee 

 with a strong and independent tendon. 



This abnormal condition of the m. ambiens, ■which seems to he 

 prevailing in Darwin's Rhea, is the intermediate stage between a 

 ty|)ically developed m. ambiens and s\ich forms in which, as in 

 Casitarius, this muscle has lost still more of its independence, and 

 then only forms an additional head of the median part of the 

 portio media m. femori-tibialis s. vasti. — Without an elaborate 

 examination and comparison of the formation of these muscles with 

 their nerve-supply, w'e should with Garrod come to the conclusion 

 that Casuarius did not possess an ambiens muscle. The assumption 

 of still further reduction of the distal portion of the m. ambiens 

 explains what I have observed in some Passerine birds, e.g. in a 

 specimen of Lanius bentet, in which the m. femoro-tibialis internus, 

 besides being strongly developed, received in its proximal part a 



