5IO 



BIRDS. 



The sternum bears a conspicuous keel, is produced 

 laterally and posteriorly into two xiphoid processes, and 

 bears articular surfaces for the coracoids anteriorly, for the 

 ribs laterally. 



The skeleton of the wing includes the stout humerus, the 

 separate radius and ulna (the latter the larger), two free 

 carpals, a carpo-metacarpus of three metacarpals fused to 

 one another and to some carpal elements, and three digits 

 — the thumb with one joint, the first finger with two joints, 

 the second with one. 



The pelvic girdle consists of dorsal ilia fused to the com- 

 plex sacral region, of ischia sloping backwards, and of pubes 

 or post-pubic processes running parallel to the ischia. Besides 

 the disposition of these three elements, the incomplete 

 ossification of the socket or acetabulum, and the absence of 

 ventral symphyses, are noteworthy. 



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

 which the proximal tarsals 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), and, finally, three toes, of which the first 

 has two phalanges, the second three, and the third four. 



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. They meet the cerebellum and throw the solid 

 optic lobes to the sides. The olfactory lobes are very 

 small. Between the cerebral hemispheres and the cere- 

 bellum, the pineal body rises to the surface, and a slight 

 posterior separation of the hemispheres will disclose the 

 region of the optic thalami. The cerebellum is ridged trans- 

 versely and divided into a median and two lateral regions. 

 It will be noted that the curvature of the brain is now well 

 marked in the adult, thus the medulla is quite hidden by 

 and descends almost vertically from the cerebellum. 



There are as usual twelve cranial nerves. 



In connection with the spinal cord, the brachial plexus 

 of nerves to the fore-arm, and the sacral plexus to the leg, 

 should be noticed. In the lumbar region the halves of the 

 cord diverge for a short distance forming a wide space — 

 the rhomboidal sinus — roofed only by the pia mater. The 



