THE ANATOMY OF BIBBS. ^ NEUROLOGY. 175 



The Bralu (Lilt, cerebrum; Gr. fyK(<pa\ov, eijlccplialon : fr<jntisp.) is the anterior dilatation 

 and complication of the main nervous axis of the body, ccjntaliied 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, C(jrresponding to what are afterward the fore- 

 brain mid-brain, and hind-brain, or prosencephalon, mesencepjhalon, -dnA opisthenceptlialon. The 

 birth and multiplication of gray neuranioebas 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 ganglicm is the cortical layer or "bark of the brain." Similar deposits of white 

 neuramcebas connect all these ganglionic colonies, furnishing the various commissures of tlie 

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

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

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

 (Utile liellies) of the brain. Actual pr(dongations of brain-tissue, or nervous threads more lilce 

 the ordinary spinal nerves, pass ont of the brain-box ; these are cerebral nerves, oftener called 

 cranial nerves ; there are twelve pairs (jf them. At the pituitary space (see p. 1.51 ; the noto- 

 chord ends just beliind it; fig. 04) is develojied a remarkable structure, the pituitary body : its 

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

 curiosity, the pinecd 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 tlie sympathetic system, 

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

 epiapopihysis 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 

 terminaMs, or terminal sheet of the brain, with wliich, morphologically speaking, the brain ends 

 in fnjut; 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 ventricles, which intercommunicate through a passage-way, 

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

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

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

 the 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 

 ganglionic thickening of its sides into what are called misleadingly the optic tJialami, since 

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

 behind the lamina tcrminalis (third ventricle, etc.) Cfimposc what is called the thalamen- 

 cephalon, 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 compf)ses the ganglionic centres called corpora bigemina, or 

 " twin bodies." These are the opitic 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 posterifir cerebral 

 vesicle (opisthencephalon) becomes separated into two parts: The fire 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"') 

 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 

 myeleneephalon, or " marrow-braiu." This descripticm i; pertinent to brains at large, repre- 

 senting the general plan <if structure; any fairly developed enccphalon shows the parts speci- 

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



