THE ANATOMY OF BIBDS. — NEUROLOGY. 181 



The Brain (Lat. cerebrum : Gr. ey/ce^aXoi/, egkephalon; frontisp.) is th<^ anterior dilatation 

 and complication tif the main nervons 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 

 (Ulterior, middle, and j)osterior cerebral vesicles, corresponding to what are afterward the fore- 

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

 birth and multiplication of gray ueuramoebas causes tliickenings 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 commissures of the 

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

 spinal chord (which was at the outset a fun-ow 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 

 tlie 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. 157 ; the note- 

 chord ends just behind it; fig. 64) is developed a remarkable structure, i\\e pituitary 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 

 otliers 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 

 l)rain, arbitrarily called the third ventricle; the anterior wall of this ventricle is the lamina 

 tcrminalis, 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 liemispheres of the cerebrum, or "halves of the 

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

 winch also leads into the third ventricle; this is the foramen of 3Iunro. Each sends out in 

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

 brain ■'). A great ganglionic thickening of gray matter in the interior of each hemisphere is 

 tlic corpus striatum; these " striped bodies " are connected by the anterior commissure of the 

 brain. The rest and greater part of the original anterior cerebral vesicle makes up by 

 j,MngUonic thickening of its sides into what are called misleadiugly the optic thalami, since 

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

 beliind the lamina terminalis (third ventricle, etc.) compose what is called the thalamen- 

 cephalon, or " bed-brain." The original middle cerebral vesicle makes up underneath into 

 longitudinal commissural fibres, called the cr\ira cerebri or " legs of the brain," ccmnecting fore 

 and aft parts ; but especially composes the ganglionic centres called corpora higemina, 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." 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 

 wliite substance (pons varolii, peduncles, etc.) and the hollow underneath it ("ff)urth ventricle") 

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

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

 myclencephalon, 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 



