SKELETON 



posterior portion, where they often take the form of prolonga- 

 tions, the extremities of which occasionally meet and enclose 

 what are called fenestras ; but these are un- 

 important when compared with the features pre- 

 sented by the anterior part. 



4. The Pectoral Arch, or 



Shoulder -Girdle, consists of 



■•-.. three pairs of bones, the 



Coracoids, the Scapulae 



or Shoulder-blades, 



'■--,^ and the Clavicles 



'■\ or Collar- 



bones, the last two usu- 

 ally coalescing in the 

 median line into a 

 V-shaped or U-shaped 

 Furcula (the well-known 

 " Merry-thought ") ; but 

 in some groups, as 

 certain Parrots, the 

 clavicles are practically 

 absent, while in others. 



Fig. 3.— Skeleton of the Limits and Tail of a Carinate '^-^ Several Owls, they do 



Bird. (The skeleton of the body is indicated by \\q^ uuitc. The furcula 

 dotted lines.) F, digits; Fi, fibula; HW, carpus; „ .^ c ^ 



J/i^, tarsometatarsus; J/7/, carpometacarpus; 0.4, Olten OSSlIieS firmly 



humerus ; OS, femur ; P,j, pygostyle ; R, coracoid ; -^yit;!! the anterior por- 

 Ul, ulna ; Sch, scapula ; St, sternum, with its keel . o ^ -i ^ i • 



(Cr) ; r, tibiotarsus ; Rd, radius ; Z, Z^, digits of tlOn of the keel, and in 



foot. (From Wiedersheim. ) Frecjata, Diclus and the 



Ratitae, the coracoids and scapulae are fused together. 



5. The Anterior Limbs, or Wings, are composed of the 

 Humerus, or upper arm - bone, the Ulna and Eadius (mak- 

 ing the fore-arm), the Carpvis or wrist, the Metacarpus and 

 Digits, corresponding with the hand and fingers. The first of the 

 three metacarpals bears the PoUex, or thumb, with one or two 



