1896.] ANA.TOMT OF THE HOATZIN. 627 



birds which, although they are certainly to be placed among the 

 HomalogonatoB and have close allies in which the ambiens is normal, 

 are themselves without it. In Nycticorax gardeni the ambiens is 

 absent ; but in two specimens that I have dissected I found a slip 

 to the flexor muscles from the fibula, similar to that in the 

 Opistliocomus here figured, although it arose rather lower down the 

 fibula. In Eclectus roratus, which again is devoid of an ambiens, 

 although many Parrots are provided with it, I found a vestige 

 almost precisely similar to that present in my second specimen of 

 Opistliocomus, in which the ambiens ended on the knee. The 

 vestige in Eclectus, as in the second Opistliocomus, consisted of 

 three slips from the fibula to the flexor tendons. This additional 

 evidence appears to me to strengthen the case for the taxonomic 

 value of the ambiens considerably. While there were known 

 only the rudiments described by me in Eclectus and Nycticorax, 

 it might have been open to doubt whether or no these really were 

 vestiges of an ambiens. Now that there have been found in different 

 individuals of Opistliocomus graded vestiges Uniting my rudimentary 

 condition with a complete ambiens, there seems no room to doubt 

 that some, at least, of the Homalogonatous birds devoid of an . 

 ambiens have once possessed it. On the other hand, I may mention 

 that although Dissura is a Stork without an ambiens, while other 

 genera of Storks possess it, in two specimens of Dissura episcopus 

 I have recently dissected I could find no trace of the vestige. 



Apart from possible systematic value, it is of intei-est to find 

 variations of so great magnitude in a few specimens of a bird. 

 Prof. Weldon has recently shown, after examination of an ex- 

 ceedingly large number of individuals of the shore-crabs, that very 

 slight deviations may be associated with a larger death-rate. In 

 the case of creatures so difficult to shoot as is Opistliocomus it may 

 be the case that those actually examined have, from the greater 

 magnitude of their variations, been less able to escape. 



In conclusion, I may place on record three minor points in the 

 myology of Opistliocomus, the only remaining features which seemed 

 to me worth recording at the present time. 



Tendons of the perforated and of the perforated and perforating 

 flexors of the third digit. — In most birds the tendons of these are 

 connected by a short stout vinculum immediately before they 

 reach the foot. Gadow mentions that this occurs in Eatites, 

 Powls, and in Pterocles. I can add to this a very long list of birds, 

 including Rliynchotus, Oliauna and Palamedea, Balearica, Psophia, 

 and Fulica. The slip is absent in Opisthocomus ; the only other 

 cases that I remember in which this occurs are Asio otus and 

 Bhytidoceros plicatus. 



Short fle.vors from the deep plantar tendons. — The tendon of the 

 flexor longus hallueis is connected with the tendon of the flexor 

 perforans by a strong vinculum and then supplies the thumb. 

 A strong muscular slip, certainly absent in most birds, leaves the 

 longus hallueis tendon immediately distal to the vinculum and runs 

 to the fourth digit. A similar muscular slip leaves the tendon of 



