744 



PHYLUM CHORDATA : CLASS AVES — BIRDS 



The hind-limb consists of a short stout femur, a tibia 

 to which the proximal tarsals (astragalus and os calcis) 



^, ■::-.:-- f^^ I Ac. ML 



Fig. 444. — Side view of pelvis of cassowary. 

 II., Iliuin ; Isch., ischium ; Pb., pubis ; Ac, acetabulum. 



are fused (forming a tibio-tarsus), 

 an incomplete fibula joined to the 

 tibia, three metatarsals fused to one 

 another and to the distal tarsals 

 (forming the tarso-metatarsus), a free 

 first metatarsal, and, finally, the four 

 toes. The first, turned backwards, 

 has two phalanges, the second three, 

 the third four, and the fourth five. 



Nervous system. — In contrast to 

 the brain of crocodiles and other 

 Reptiles, the brain of the pigeon and 

 other Birds fills the cranial cavity. 

 The cerebral hemispheres are large 

 and smooth. Their roof is thin, their 

 main mass consists of the large corpora 

 striata which bulge into the ventricles. 

 They meet the cerebellum and throw 

 the solid optic lobes to the sides. 

 The olfactory lobes are very small 

 (cf. deficient sense of smell). Between 

 the cerebral hemispheres and the 

 cerebellum, the pineal body rises to 

 the surface, and a slight posterior 

 separation of the hemispheres will 

 disclose the region of the optic 

 thalami. The large cerebellum is 



Fig. 445. — Bones of 

 hind-limb of eagle. 



/., Femur ; t.t., tibio-tarsus ; 

 fb., fibula ; a., ankle- 

 joint ; m.t., tarso-meta- 

 tarsus ; m.f., first meta- 

 tarsal (free). 



