NERVOUS SYSTEM. 87 



Prey, while they present in the Pigeons and Passeres a toler- 

 ably uniform and rounded aspect. Their surface is either quite 

 smooth, or exhibits only simple inflexions, or several shallow depres- 

 sions, as in the Parrots. They appear to terminate abruptly be- 

 hind, so as to. leave the small cerebellum completely uncovered. 

 The cerebellum, as it is called, would seem to correspond rather 

 with the vermiform process of that organ in the Mammalia, here 

 increased in size, and its hemispheres, to a pair of lateral projec- 

 tions or appendages of the same. This process is divided into a 

 considerable number of lamellae (20 to 30), which vary in different 

 genera. A longitudinal section exposes in its interior the arbor 

 vitae, the ramifications of which vary numerically according to the 

 genera, they being 9 in Lanius, 11 in the Falcon ; the corpora den. 

 tata cerebelli are, however, wanting. There is no distinct connect- 

 ing commissure to the lateral lobes, or pons, its place being supplied 

 only by some transversal medullary fibres. The corpora quadri- 

 gemina are represented by a single pair of convex eminences, pre- 

 senting externally no indicatipns of a further division, and which, 

 placed tolerably apart from each other, are interposed between the 

 cerebral hemispheres and cerebellum. They are composed exter- 

 nally of white or medullary substance, but have internally a large 

 nucleus of gray matter, enclosing a small cavity or ventricle. 

 The thalami optici of smaller size are partly united with these bige- 

 minal bodies, and partly lodged within the hemispheres of the 

 cerebrum. The corpora striata form a pair of large ganglia. Su- 

 periorly and posteriorly, in the angle between the cerebellum and 

 its two hemispheres, the pineal gland is situated as a tongue-shaped 

 lobule, in general placed quite superficially, though its position in 

 the Owls is deeper. It is easily removed along with the dura 

 mater in stripping off that membrane. The pituitary body lies in 

 a depression of the sella turcica of the sphenoid bone, and is of 

 considerable size. Of the commissures, the great or corpus callo- 

 suin is extremely short and small, and the part corresponding with 

 the fornix is in an equally .rudimentary condition. These parts have 

 in fact all but coalesced with the anterior commissure, from which 

 a radiated expansion of medullary fibres may be seen, upon drawing 

 the hemispheres asunder, to be prolonged into their substance. 

 Several streaks of gray and white matter lying further back behind 

 this, correspond to the commissura mollis and posterior, which over- 

 lie the large valvula cerebelli. The ventricles of the brain are essen- 

 tially the same as in the Mammalia, only the lateral ventricles have 



