670 



NERVOUS SYSTEM. (NERVOUS CENTRES. THE ENCEPHALON.) 



ingenuity he ascribes the passage of the nervous 

 force (under the name of animal spirits) from one 

 part to another, to the anatomical relations of 

 those parts, and the direction of the consti- 

 tuent fibres. And, indeed, we may find in the 

 writings of this great man the germs of many 

 a theory which, in our own times, has been 

 brought forward with a more plausible aspect, 

 disencumbered of the quaint phraseology and 

 superabundant metaphor so common in his 

 day. I shall quote one remarkable instance 

 as very much in point. Speaking of the fourth 

 pair of nerves as connected with the corpora 

 quadragemina, he says : " Concerning these 

 little nerves it is observed, that when (although) 

 many others proceed from the sides or the basis 

 of the oblong marrow, these arise from the 

 aforesaid Prominences in the bunching forth at 

 the top (nates and testes). The reason of which, 

 if I be not mistaken, is this, we have affirmed 

 that these prominences do receive and commu- 

 nicate to the brain the natural instinct delivered 

 from the heart and bowels to the cerebel ; and 

 on the other side, or back again, do transfer 

 towards the Proecordia, by the mediation of the 

 cerebel, the forces of the passions or affections 

 received from the brain ; but in either action 

 the motion of the eyes is affected with a certain 

 manifest sympathy. For if pain, want, or any 

 other signal trouble afflicts the viscera or the 

 praecordui, a dejected and cast-down aspect of 

 the eyes will declare the sense of its trouble : 

 when on the contrary, in joy, or any pleasant 

 affection of the prtecordia or viscera, the eyes 

 are made lively and sparkle again. In like 

 manner the eyes do so clearly show the affec- 

 tions of the mind, as sadness, anger, hatred, 

 love, and other perturbations, that those who 

 are affected, though they should dissemble, 

 cannot hide the feeling and intimate concep- 

 tions of the mind. Without doubt these so 

 happen because the animal spirits tending this 

 way and that way in this deviating place be- 

 tween the brain and the przecordia, do at once 

 strike those nerves as the strings of a harp. 

 Wherefore, from this kind of conjecture, which 

 we have made concerning the use of these 

 nerves, we have called them Pathetical, al- 

 though indeed other nerves may deserve the 

 same name."* 



Malpighi and Vieussens were well acquainted 

 with the fibrous structure of the brain, and 

 appear to have had very correct notions as to 

 the general direction which they assume, and 

 the parts which they serve to connect to each 

 other. The former describes the fibres of the 

 brain and cerebellum as taking their origin 

 from the trough of the spinal marrow contained 

 within the cranium (tnedulla oblongutu); " for 

 they ramify from four reflected crura of this 

 medulla in all directions, until they end by their 

 branched extremities in the cortex." Vieus- 

 sens states that the medullary substance is com- 

 posed of innumerable fibrils connected together 

 and arranged into various fasciculi, which be- 

 come very obvious when it is boiled in oil.-f 



* English edition of Willis's Works, p. 90, fol. 

 Lond. 1684. 



f Malpighi, Exercitatio Epistolica dc Cerebro, 



The great merit of Reil, Gall and Spuvzheim, 

 and their followers in later years, consists in 

 their having followed out with great diligence 

 the coarser anatomy of those fibres, and deter- 

 mined many important and undeniable truths. 

 But in the statements of all anatomists, who 

 avail themselves of no other aid than that 

 which the naked eye affords, there is much that 

 must necessarily be uncertain or doubtful, nor 

 is there any other mode of removing these un- 

 certainties but by the successful application of 

 microscopical analysis to the whole cerebral 

 structure. 



Of the surface of the encephulon We no%v 

 proceed to examine the various points worthy 

 of notice in the superficial anatomy of the 

 encephalon. 



The shape of the brain is determined by that 

 of the cerebral hemispheres. A line drawn 

 around the surface of the latter, so as to enclose 

 them, would describe an oval, the smaller ex- 

 tremity of which is directed forwards. 



The superior and lateral surfaces of the 

 encephalon are convex, and have a smooth 

 appearance from the visceral layer of the arach- 

 noid being extended over them, adhering to the 

 subjacent pia mater. When the membranes 

 have been removed, the convoluted character 

 of these surfaces, previously seen through them,, 

 becomes very manifest, as will be more parti- 

 cularly described by-and-bye. The longitudinal 

 and transverse diameters of these surfaces cor- 

 respond to those of the cranial cavity. 



The superior surface is divided along the 

 median plane into two equal and in a great 

 degree symmetrical portions by a fissure which 

 passes vertically between them and receives the 

 great falciform process of the dura mater. In 

 front and behind, this fissure completely divides 

 the central lobes. In the latter situation, the 

 tentorium cerebelli is seen at the bottom of 

 it when the hemispheres are separated, if the 

 encephalon be in situ; if it have been removed, 

 however, the superior surface of the cerebellum 

 forms the floor of the fissure. In the middle 

 the fissure is interrupted by a horizontal lamina 

 of white fibres, which is called the corpus cal- 

 loau/n, the great commissure of the cerebral 

 hemispheres. 



The inferior surface of the encephalon also r 

 called commonly the base of the brain, pre- 

 sents many points worthy the attention of the 

 anatomist. 



It is not all upon one level : in this respect 

 it corresponds with the disposition of the base 

 of the skull. We find, indeed, three segments,, 

 each on a different plane, and corresponding to 

 each of the three fossae of the cranium. This 

 is best observed by examining a vertical section 

 of the head, the brain being retained in its 

 situation, or by removing the wall of the cra- 

 nium on one side quite down to its inferior 

 surface. 



The anterior segment, and that which is on 



1664. Vieussens, Neurographia Universalis, lib. i. 

 cap. x. See the whole passages quoted in Dr.. 

 Gordon's Observations on the Structure of the Braiu. 

 Edin. 1817, p. 21. 



