442 



Vertebrata. 



"well-developed crest (a similar crest occurs in the Dinosaurians, but 

 is very feeble in other Eeptile.s) . There is usually a patella. The 

 structure of the tarsus is interesting. As in the Reptiles, it is 

 divided into proximal and distal portions, between which there is 

 a very perfect joint ; the tarsals of the proximal row are distinct from 

 the tibia in the young animal, but in the adult are fused so as to leave 

 no trace. In the same way, the distal portion fusoH with the meta- 

 tarsus, so that in the adult there is apparently no tarsus. The foot 

 never consists of more than four toes, there is never any trace of 

 the fifth or of its metatarsal. Metatarsals two, three, and four, 

 are long, and only separate in the embryo ; later they fuse almost 

 down to the toes, forming a long thin bone (the tarso-metatarsus) ; 

 on the other hand, the first metatarsal is separate, but much shorter 

 than the others, and attached to these at its distal end. The hallux 

 which is usually directed backwards, consists of two phalanges, 

 the second digit of three, the third of four, and the fourth of five' 

 (as a rule) ; all as in Lacertilia and Dinosauria. Of the forwardly 

 directed toes the middle one (No. 3) is usually the longest; the 

 hallux may be large, but is often rudimentary or absent. 



The brain, in comparison with that of the Reptiles, is large. 

 The hemispheres, especially, are well developed ; the c e r e - 



Fig. 370. Brain of a Pigeon, dorsal (A), and ventral (B). h cerebellum, 

 / cerebrum, Ic epiphysis, I olfactory lobes, mi mid-brain, r spinal cord, s optic nerre, 

 t hypophysis. — After Jeffery Parker. 



b e 1 1 u m is likewise large ; its median portion, which is elongate, and 

 furnished with deep transverse furrows, covers both the medulla and 

 the middle portion of the mid-brain, the two lobes of which are 

 pushed out to the sides. Of living Reptiles, the Crocodiles come 

 nearest to the Birds in regard to the development of the brain. 



The olfactory organ is very like that of Lizards; the 

 external nares, on account of the length of the premaxillae, are usually 



