NERVOUS CENTRES. (HUMAN ANATOMY. THE MENISGES.) 



be attached in a cluster to the same stem. The 

 fact that epithelial particles may be seen upon 

 the surface of the membranous sac of some of 

 the bodies is sufficient proof that it is derived 

 from arachnoid membrane. If this be ad- 

 mitted, then it seems impossible to come to 

 any other conclusion than that the pia mater is 

 the seat of the primary deposit, and this opi- 

 nion is confirmed by the fact that we meet with 

 the Pacchionian bodies on the internal pro- 

 cesses of the pia mater, when we have no evi- 

 dence of the existence of arachnoid membrane. 



Or it might be conjectured that these bodies 

 indicate a degenerate condition of the elemen- 

 tary particles of the superficial layer of the grey 

 matter of certain convolutions, produced by 

 frequent irritation. 



Are the Pacchionian bodiesnatural structures? 

 The great frequency with which these bodies 

 are met with in the various situations above- 

 mentioned, lias induced many, even in the 

 present day, to regard them as normal struc- 

 tures, the physiological office of which is as 

 yet unknown. But there are many facts which 

 strongly militate against such a conclusion. In 

 the first place it may be observed that Pacchi- 

 onian bodies never occur in the earliest periods 

 of life. In the course of a long experience in 

 anatomical investigations I have never seen 

 them at a period antecedent to six years. The 

 brothers Wenzel, who made a series of special 

 examinations with a view to determine this 

 question, make the following statement. In 

 children, from birth to the third year, these 

 bodies, if they ever occur, must be very few. 

 From the seventh to the twentieth year they 

 sometimes are numerous. From the latter pe- 

 riod to the fortieth year their number is consi- 

 derable, and the nearer we approach the fortieth 

 year the greater does it become. Lastly, from 

 the fortieth to the one hundredth year these 

 bodies are found in great numbers. 



It must be further remarked that even at 

 those periods of life when the Pacchionian 

 bodies are found in greatest numbers, cases fre- 

 quently occur in which no trace of them can 

 be found. There is likewise the greatest variety 

 as to their number and size, in different indivi- 

 duals of the same age. 



It has always occurred to me to find them 

 most numerous in cases where I had reason to 

 know that the brain had been subject to fre- 

 quent excitement during life. In persons ad- 

 dicted to the excessive use of spirituous liquors, 

 in those of irritable temperament and who were 

 frequently a prey to violent and exciting passions, 

 they are almost uniformly highly developed. 



The Pacchionian bodies are peculiar to the 

 human subject. Nothing similar to them has 

 been found in any of the inferior classes of 

 animals. 



In reference, then, to the question, what is 

 the nature of these bodies, I have no difficulty 

 in stating my opinion that the evidence greatly 

 preponderates in favour of their morbid origin ; 

 that they are the product of a chronic very 

 gradual irritation due to more or less frequent 

 functional excitement of the brain itself. It is 

 not unlikely that the friction to which the 

 opposed surfaces of the arachnoid are conti- 



645 



nually subjected in the movements of the 

 brain, especially when they are of a more rapid 

 and violent kind, as under states of cerebral 

 excitement, may contribute to the develope- 

 merit of many of the appearances connected 

 with these bodies. The opaque spots which 

 are of such frequent occurrence upon the sur- 

 face of the heart may be quoted as an example 

 of a morbid change, very commonly met with, 

 and resulting probably from the friction against 

 each other of opposed serous surfaces. Were 

 the Pacchionian bodies normal structures, they 

 would not be so frequently absent from brains 

 which afforded every other indication of being 

 in a healthy state ; nor should we find opacity 

 of the arachnoid (a decidedly unhealthy con- 

 dition) so commonly coexistent with the full 

 developement of them. Again, were they 

 a necessary part of the healthy organism, we 

 might expect to find them more constant as 

 regards size, number, and the extent of surface 

 over which they were placed. 



Of the ligamentum dentatum (serrated 

 membrane of Gordon). This structure forms 

 a part of the mechanical arrangements con- 

 nected with the spinal cord and the roots of its 

 nerves. It is found in the subarachnoid 

 space, adhering on the one hand to the pia 

 mater, and, on the other, attached at certain 

 intervals to the dura maler. 



The ligamentum dentatum consists of a nar- 

 row longitudinal band, adhering by its inner 

 straight border to the pia mater on each lateral 

 surface of the spinal cord, midway between 

 the anterior and posterior roots of the spinal 

 nerves, reaching from the highest point in the 

 cervical region down to the filiform prolongation 

 with which it becomes incorporated. Its outer 

 border exhibits a series of tooth-like trian- 

 gular processes which are inserted by their 

 apices into the dura mater. The first pointed 

 process, which is longer than the rest and less 

 triangular in shape, is inserted into the dura 

 mater on the margin of the occipital bone, 

 where it stands in relation with some parls of 

 interest. The posterior root of the sub-occi- 

 pital nerve, and the filaments of origin and the 

 resultant trunk of the spinal accessory, are on a 

 plane posterior to it. The vertebral artery and 

 the ninth pair of nerves are anterior to it. The 

 number of teeth varies from eighteen to twenty- 

 two. The last is attached to the dura mciter 

 about the level of the first or second lumbar 

 vertebra. The points of attachment are be- 

 tween the points of exit of the spinal nerves 

 being almost always nearer the lower than the 

 upper nerve. The intervals between each pair 

 of dentated processes vary in different regions of 

 the spine as the disiunces between the roots 

 of the nerves vary. At its insertion info the 

 dura mater each process pins down the visceral 

 and parietal layers of the arachnoid membrane, 

 probably piercing them to reach the fibrous 

 membrane. At its lowest part, a little above 

 the extremity of the cord, the denticulated 

 margin ceases, and the longitudinal portion 

 may be traced downwards, gradually dimi- 

 nishing in size, along each side of the filiform 

 prolongation of the pia mater. 



The dentated ligament has to the naked eye 



