446 STRUCTURE AND OLASSIFTOATION OF BIRDS 



as well as posterior; in Daption capensis, and in many 

 others, the spines are confined to the hind margin of the 

 organ. The more usual condition is the intermediate 

 form. 



There is a well-developed but small gizzard present. 

 The cceca are absent in the Oceanitidse, but present, as a 

 rule, in the Procellariidee ; they are small and nipple-like, 

 and in Cymochorea appear to be reduced to a single caecum. 



The gall bladder is 

 always present, and the 

 lobes of the liver are 

 equal or nearly so. The 

 arrangement of the 

 intestine is shown in 

 fig. 210. The duodenal 

 loop is double ; the 

 greater part of the in^ 

 testine is drawn out into 

 a considerable number 

 of straightish loops. 



As to muscular 

 anatomy, the great 

 pectoral is divisible into 

 two layers by an inter- 

 posed tendon, as in storks 

 and Steganopodes. But in Larus, according to Fubbeingeb 

 (and in Podica also), the same division occurs, which tends 

 to lessen the differences between the Tubinares and the 

 Laridse, so insisted upon by G-aeeod, Eoebbs, and some 

 others. The tensores patagii in the Tubinares are com- 

 plicated, but not in all the genera. In the Oceanitidae they 

 are simplest. In these petrels the tensor brevis is a simple 

 tendon. In Pelecanoides, and in some others, there is the 

 additional complication that the tendon bifurcates near to 

 its attachment on the extensor tendon, and gives off an 

 anterior slip inserted more wristwards. In Prion affairs 

 are still further complicated by the metamorphosis into 

 tendon of the whole of the extensor metacarpi radialis 



Fig. 



210. — Intestines of Fulmarus glacia- 

 lis (after Mitchell). 

 x, short-circuiting vessel divided. 



