Characteristics of the Vertehrata. li 



cliarrue ' for the support of the ' reetrices ' feathers. The two 

 anterior ribs having- often no sternal element^ the character of 

 ' dorsal ' or ' cervical ' comes to depend upon the relation these 

 movablj articulated appendages hold to the subjacent lung. In 

 the Ratitae, the osseous system of which order shows many Rep- 

 tilian affinities^ the cervical ribs often remain unanchylosed for 

 considerable periods of their adult life. ' Processus Uncinati ' are 

 attached by ligament or anchylosed to the dorsal ribs, with the 

 exception of the first and last. The largely developed sternum 

 gives support to the strong coracoids anteriorly, and to the ossified 

 sternal elements of the costal arches laterally, but it is never pro- 

 longed outwards at its posterior angles into costal processes as in 

 Reptiles, The clavicles are occasionally absent, but ordinarily form 

 a fureulum by fusion at their anterior extremities, with which, as 

 also with their uj)per ends, elements segmented off from the cora- 

 coids are found to anchylose. The iliac bones extend so far forwards 

 as to overlap some of the ribs, so that no distinct lumbar region 

 exists. The ischiac and pubic bones are prolonged backwards, so 

 as to be approximately parallel with each other and with the long 

 axis of the body ; except in Rhea, the ischia never form any sym- 

 physis ; nor do the pubic bones, except in Struthio Camelus. The 

 femur moves in the acetabulum in a direction parallel with that of 

 the long axis of the body. The fibula never reaches the ankle 

 joint, which is situated as in Reptiles between the proximal and 

 distal row of the tarsus. In adult Birds, the tibio-tarsus and the 

 tarso-metatarsus are each perfectly anchylosed into a single bone. 

 This is not the case in Reptiles. Tlie external toe is never present 

 in Birds. The hallux is sometimes absent; when present, it is 

 carried upon a metatarsal articulated to the tarso-metatarsus near 

 its distal extremity, and consists of two phalanges. In the Ostrich, 

 both hallux and index are absent, as well as the fifth toe, and the 

 foot is reduced to the didactylous condition, though the tarso- 

 metatarsus retains a rudiment of the third distal articular trochlea. 

 Dental papillae, with caps of dentine, have been observed in the 

 embryoes of Psittacidae ; in adult Birds, the digestive tract is 

 characterized by the absence of teeth, of lips, and of a velum 

 pendulum palati ; and by the presence of a horny beak, and of a 

 muscular gizzard placed posteriorly to a glandular proventriculus. 

 With the absence of comminuting organs anteriorly to the gizzard, 



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