644 DR. p. CHALMEBS MITCHELL OS THE [])ec. 1 7, 



o£ the humerus. In the other forms, eutaxic or diastataxic, the 

 muscle reaches to the end of the third quarter (text-figs. 77 & 

 78, D.). Thus there exists a general correlation between the 

 apocentricity of the wing and the apoeentricity of this muscle. 

 It is least apocentric in certain diastataxic forms, most apocentric 

 in certain eutaxic forms, intermediate in others. 



Scapuli-lmmerales anterior et posterior. — The posterior muscle, 

 commonly termed the teres major, is present in all the Gruiformes. 

 It is much larger than the anterior muscle and runs from an 

 extensive origin on the scapula to converge in a tendon which is in- 

 serted to the median process of the humerus (text-figs. 74 & 75, /S'.P.) . 

 Its size apparently is subject to individual variation ; for in Aramus 

 and in Psophia Fiirbringer found it relatively small, while in my 

 specimens of these birds I found it very large, at least as large as 

 in any other members of the group. In Balearica alone I found 

 it small. Upon its size, no doubt, depends its contact with or 

 distance from the anterior muscle, conditions the varying nature 

 of which have been described by Fiirbringer. 



The anterior muscle arises from the proximal portion of the 

 scapula and runs across the angle between the scapula and the 

 humerus to its insertion on the humerus near the forked origin of 

 the anconaeus humeralis. Its maximum development in the group 

 appears in the Eallidse (text-fig. 74, S.A.), where, although much 

 narrower than the posterior muscle, it is a good strap of fleshy tissue. 

 In the Gruinse it is relatively as large as in the Hallidge, and its fibres 

 converge to a strong tendon. In the other diastataxic forms it is 

 much reduced : thus in Aramus and Etirypyga, Fiirbringer found it 

 present but well separated from the posterior muscle, and small, 

 while in my specimens the muscle was represented only by a few 

 fibres. In Otis it is much reduced, and is attached to the humeral 

 anchor of the anconaeus scapularis. In all the eutaxic forms either 

 it displays a very marked reduction or is absent. Thus in Psophia 

 ohscura (text-fig. 75, S.A.) I found it much reduced and chiefly 

 tendinous; in Psophia leucoptera it was absent, and Fiirbringer 

 states that it is missing in the genus. In Cariama and Chunga 

 and in Rhinochetus it is absent ; in Ileliornis it is present, but 

 much reduced. 



It is probable that the existence of a separate anterior and 

 posterior scapuli-humeralis is due to the segmentation of a primitive 

 Reptilian single muscle, and the absence of one of the portions 

 normal in birds might therefore be ancestral or archecentric, the 

 single muscle being the undivided representative of the Eeptilian 

 prototype. The series of conditions among the Gruiformes, how- 

 ever, make it plain that the presence of both muscles is the normal 

 and archecentric condition for the assemblage, and that the loss, 

 partial or complete, of the anterior muscle is an apocentric 

 modification. It is to be noticed, therefore, that here is a fairly 

 definite case of correlation of apocentricities. The anterior division 

 is small or absent in all the eutaxic forms ; it is well developed 

 only in the diastataxic forms ; but the correlation is not exact, for 



