THE ANATOMY OF BIBDS. — NEUROLOGY. 175 



The Brain (Lat. cerebrum; G-r. eyxei^aXoi/, egkephalon; ftontisp.) is the anterior dilatation 

 and complication of the main nervous axis of the body, contained within the skull. It resembles 

 a soap-bubble blown at the end of a pipe, being not less beautiful in its iris-quality, and not less 

 lasting. It is primarily triune, or three-fold, beginning as three such bubbles, called the 

 anterior, middle, and posterior cerebral vesicles, corresponding to what are afterward the fore- 

 brain, mid-brain, and hind-brain, ov prosencephalon, mesencephalon, and opisthencephalon. The 

 birth and multiplication of gray neuramoebas causes thickenings of the bladdery membranes in 

 various places and ways ; all such gray deposits are the ganglia of the brain, and the great 

 peripheral ganglion is the cortical layer or "bark of the brain." Similar deposits of white 

 neuramcebas connect all these ganglionic colonies, furnishing the various eommisswres of the 

 brain. The cavity of the original bubbles, continuous with the hollow of the pipe-stem or 

 spinal chord (which was at the outset a furrow along the back of the embryo, not a tube) 

 becomes partially divided up into several communicating hollows ; these are the ventricles 

 (little bellies) of the brain. Actual prolongations of brain-tissue, or nervous threads more 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 (see p. 151 ; the noto- 

 chord ends just behind it; fig. 64) is developed a remarkable structure, ^ihe pitidtary body : its 

 nature is unknown. This lies under the brain ; opposite it, on top of the brain, is another 

 curiosity, the pineal body ; it has been considered the special seat of the soul by some, though 

 others have located that throne of animal grace in the solar plexus of the sympathetic system, 

 which is in the belly. The pituitary and pineal are also called respectively the hypapophysis and 

 epapophysis 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 

 terminaUs, or terminal sheet of the brain, 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 cerebrium, or "halves of the 

 great brain " ; they retain their ventricles, which intercommunicate through a passage-way, 

 which also leads into the third ventricle ; this is the foramen of Mwn/ro. Each sends out in 

 front a hoUow process; these processes are the olfactory lobes, or rhinencephalon ("nose- 

 brain "). A great ganglioiuc thickening of gray matter in the interior of each hemisphere is 

 the corpus striatum; these " striped bodies " are connected by the anterior commisswre 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 is called the thalamen- 

 eephahn, or " bed-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 (Sailed corpora bigemima, or 

 " twin bodies." These are the optic 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." yhe 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 

 white substance (pons varolii, peduncles, etc.) and the hollow underneath it ("fourth ventricle") 

 eonstitutes the rrietemephalon or " after-brain." The hind part of it tapers off into the spinal 

 chord; this tapering part is the mMulla oblongata, or "oblong marrow," also called the 

 myekncephahn, or " marrow-brain." This description is pertinent to brains at large, repre- 

 senting the general plan of structure ; any fairly developed encephalon shows the parts speci- 

 fied ; and most complicated brain, as that of man, only shows what elaborate finishing touches 



