1901.] 



ANA-TOM Y OF GEUirOBM BIEDS. 



651 



the tibial belly of the gastrocnemius after a short separate course. 

 The Otis type occurs iu Otis, in the GrruinsB, PsophiiDse (but in the 

 latter the middle head of the gastrocnemius is double), in the 

 Dicholophidae, in RJivnochetus, aud in Eurypyga, except that the 

 isehio-flexorius in most cases is better separated from the under- 

 lying masses and appears to run straight to the tibia, merely 

 receiving on its way a tendinous slip from the raphe of the two 

 portions of the caud-ilio-flexorius. 



Text-fig. 83 



Text-fig. 84. 



FMVBL 



SOL.-^'. 



ICaee-muscles of Otis tarda. Knee-muscles of Hdiornis fiilica. 



Description and lettering as in text-flgui-es 81 & 82. 



(4) Heliornis type. This type is peculiar to the group. 1 

 describe it from Heliornis (text-fig. 84), but I gather from Beddard's 

 description that the condition in Podica is similar. The caiid-iho- 

 fiexorius is devoid of the normal femoral insertion, and the 

 gastrocnemius has no posterior femoral head. The caud-ilio- 

 flexorius and the isehio-flexorius end in flat tendons to the tibia 

 inserted very closely together. 



In most respects the final interpretation of these four 

 types in terms of archecentricity and apocentricity must await 

 further knowledge. It is clear, however, that the condition in 

 Heliornis, a eutaxic form, is the most apocentric. Comparative 

 anatomy shows plainly that the existence of a femoral insertion 

 of the caud-ilio-flexorius (accessory semi-tendinosns) is arche- 

 oentric in birds, and its loss must be regarded as an apocentric 

 modification. The great width of this femoral insertion in 

 Ballus and Aramus, two diastataxic forms, would appear to 

 be archecenti'ic. The placing of the Otis type and its modifica- 

 tions depends partly on the interpretation of the morphological 

 nature of tiie i)osterior femoral head of the gastrocnemius. On 



