SEC. IV ANATOMY OF BIRDS 259 



communicating hollows ; these are the ventricles (little bellies) of the 

 brain. Actual prolongations of brain-tissue, or nervous threads like 

 the ordinary spinal nerves, pass out of the brain-box ; these are 

 cerebral nerves, oftener called cranial nerves ; there are twelve pairs 

 of them. At the pituitary space, just behind which the noto- 

 chord ends (see Fig. 64), is developed a remarkable structure, the 

 pituitary body : its nature is unknown. This lies under the brain ; 

 opposite it, on top of the brain, is another curiosity, the couarium or 

 pineal body ; it has been considered the special seat of the soul by 

 some, though others have located tliat throne of animal grace in the 

 solar plexus of the sympathetic system, which is in the belly. It 

 is probably the remains of an extinct eye. The pituitary and 

 pineal are also called respectively the hypophysis and epiphysis 

 cerebri. They lie respectively at the bottom and top of one of the 

 cavities of the brain, arbitrarily called the third ventricle; the 

 anterior wall of this ventricle is the lamina terminalis, or terminal 

 sheet of the bi-ain, with which, morphologically speaking, the brain 

 ends in front; though, in its actual growth, the prosencephalon 

 crowds ahead of this formation. As the brain-cells multiply, the 

 prosencephalon outgrows the associated parts, and becomes nearly 

 separated into lateral halves ; these are the hemispheres of the 

 cerebrum, or " halves of the great brain " ; they retain their ven- 

 tricles, which intercommunicate through a passage-way, which also 

 leads into the third ventricle ; this is the foramen of Monro. Each 

 sends out in front a hollow process ; these processes are the olfactory 

 lobes, or rhinencephalon ("nose-brain"). A great ganglionic thicken- 

 ing of gray matter in the interior of each hemisphere is the cmpns 

 striatum ; these " striped bodies " are connected by the anterior com- 

 missure of the brain. The rest and greater part of the original 

 anterior cerebral vesicle makes up by ganglionic thickening of its 

 sides into what are called misleadingly the optic thalami, since these 

 tracts have nothing to do with the sense of sight. The thalami and 

 associate parts behind the lamina terminalis (third ventricle, etc.) 

 compose what some call the thalamencephalon, or " bed-brain," others 

 the dienccp)halon, or " 'tween-brain." The original middle cerebral 

 vesicle makes up underneath into longitudinal commissural fibres, 

 called the crura cerebri, or " legs of the brain," connecting fore and 

 aft parts ; but especially composes the ganglionic centres called cor- 

 'pora bigemina, or "twin bodies." These are the op>tic lobes, or "eye- 

 brain." They are connected by transverse commissure. The optic 

 ganglia and commissure, the cerebral crura, and contained cavities, 

 essentially compose the mesencephalon, or "mid-brain." The original 

 posterior cerebral vesicle (opisthencephalon) becomes separated into 

 two parts : the fore part of it is moulded into the considerable mass 

 of the cerebellum (" little brain ") ; which, with its connections of 



