140 BULLETIN UNITED STATES GEOLOGICAL SURVEY. \Tol.YI. 



The clavicles are thoroughly fused together, forming one deeply XT- 

 shaped bone; their cylindrical and curved lengths support at the union, 

 mesially and below, a long lamina of bone, in the median ijlane, that is 

 directed upwards and backwards, parallel to the anterior carinal crest, 

 to which it is united by ligament in the living bird. Their upper ends 

 are expanded and placed in the skeleton flat-wise against the acromial 

 process of the scapula and the head and the lower or clavicular process 

 of the coracoid. The acromial process, through its bifurcation, partially 

 grasps the hind border of this expanded end of the furculum, on either 

 side. 



This bone seems to be non-pneumatic, while the coracoids are hollow 

 almost throughout their entire extent, having in their composition very 

 little cancellous tissue and a thin though firm, compact layer. The scap- 

 ulae are hollow for some little distance into their blades, to be terminated 

 by a cancellous structure, with an external and attenuated outer compact 

 coat. 



With the scapula arch in situ, we observe that the coracoids do not 

 meet below in the coracoidal groove of the sternum, but approach only, 

 on each side, as far as the periphery of the i)neumatic foramen at the 

 base and behind the manubrium. 



They are directed upwards, forwards, and outwards, at an angle of 

 about 45° with the horizontal plane, the skeleton being erect; and, as a 

 consequence, we find their upper ends further apart than any other part 

 of the bone. 



The aperture between scapula and coracoid is in nearly a right angle, 

 and the straight part of the inner scapular borders are parallel, their 

 obliquely cut ends alone slightly turning outwards. 



A scapula is 2.5 centimetres long, a coracoid 3 centimetres, the in- 

 tercla\acular space above being 1 centimetre. 



In Turdus migratorius, as j)erhaps the best representative of avian 

 structure among the Oscines, we find the scapula shorter in proportion 

 when compared with the other bones of the arch ; the coracoids more 

 depressed, i. e., more in line with the sternum ; and the furculum in its 

 direction backwards showing a gentler curve. 



TJie upper extremity — (PI. lY, Figs. 22, 31, 36, and 43).^ — The pectoral 

 limb in Eremopliila maintains the usual ornithic characters of a great 

 number of the class, both in arrangement and number of the bones com- 

 prising it. The skeleton arm has ten distinct segments ; of these, we 

 find one devoted to the brachium, two to the carpus, one to the metacar- 

 pus, and four to the phalangeal portion of the manus. 



In ornithotomy we find the head of the os humeri playing in a shallow 

 glenoid cavity, composed of the glenoid process of the scapula, the hu- 

 meral facet of the coracoid, and here, in addition, the os humero-scap- 

 ulare ; the homologue of the humerus summus not entering into the 

 scapulo-humeral articulation as an overarching and protecting process, 

 as we find it in human anatomy. 



