NERVOUS SYSTEM. (J\ T ERVE.) 



characters, with the peculiar construction of 

 the peripheral expansion, would induce me to 

 regard what is generally described as the optic 

 nerve as a process of the brain itself, around 

 the peripheral portion of which a dioptric appa- 

 ratus has been disposed in order to produce 

 those refractions in the rays of light which are 

 necessary to the formation of an image upon the 

 retina. And my friend, Mr. Bowman, has been 

 Jed to adopt a similar conclusion from examin- 

 ing the structure of the retina and optic nerve. 



Olfactory nerves. The true olfactory nerves 

 are very numerous and pass from the bulb of the 

 olfactory process or olfactory nerve of descrip- 

 tive anatomists. The peculiar characters of this 

 process, as distinguishing it from a nerve properly 

 so called, have long attracted attention. In truth, 

 this process has the characters of a portion of 

 the brain in a much more obvious way than the 

 optic nerve, for it contains a larger portion of 

 grey matter which adheres as a distinct layer to 

 the white matter, as in the formation of the 

 convolutions ; and, moreover, its anterior ex- 

 tremity or bulb contains a ventricle which may 

 easily be demonstrated in a recent brain. It is 

 from this bulb that the minute threads, which 

 may be properly called olfactory nerves, take 

 their rise and pass down through the foramina 

 of the cribriform plate. Nothing satisfactory 

 is known as to the disposition of the ultimate 

 ramification of these nerves upon the Sclmei- 

 derian mucous membrane. The statement of 

 Valentin that they form loops similar to those 

 of cutaneous nerves is probably correct. It is 

 not improbable that the papillae described by 

 Treviranus were particles of columnar epithe- 

 lium to which cilia are attached. 



Auditory nerve. The auditory nerve exhibits 

 characters sufficiently distinct from the portio 

 dura of the seventh, beside which it lies, to have 

 led the anatomists of former days to separate it 

 under the name of portio mollis. In fact, it pos- 

 sesses all the appearance of cerebral substance, 

 and it wants the fasciculated disposition which 

 mere nerves exhibit. Its fibres are delicate 

 and very prone to become varicose, and, as in 

 the case of the olfactory process, it passes out 

 of the cranium, not as a trunk, but by means 

 of several minute filaments of various size 

 which pierce the foramina of the cribriform 

 floor of the internal auditory foramen. Most 

 observers express themselves in favour of the 

 opinion that the terminal filaments are disposed 

 in a looped form upon the membranous laby- 

 rinth and the cochlea. Valentin describes and 

 delineates a plexiform arrangement, with loop- 

 ings of some of the primitive fibres; others ofthem, 

 however, he says, do not affect this disposition, 

 but appear to have free extremities. And this de- 

 scription corresponds with that which Henle has 

 given. This author states that from researches 

 which he has made upon the lamina spiralis of 

 mammifera and the ampullae of the frog, he has 

 no doubt of the existence of fibres which pass 

 from one fascicle to another in a looped form ; 

 but he finds it difficult to determine whether all 

 the tubes contained in each fascicle form 

 similar loops. Wagner delineates the looped 

 arrangement, and Pappenheim adopts the 

 same view. Mr. W barton Jones states that 



597 



the tubular structure of the nervous fila- 

 ments ceases among grains of nervous matter, 

 arranged into a sort of expansion, (see ORGAN 

 OF HEARING), and he denies the existence of 

 an arrangement in loops. My own observation 

 leads me to concur in this description ; and I 

 would add that there seem to be here, as in the 

 retina, some elements of the grey nervous 

 matter scattered among the primitive filaments. 

 This fact did not escape Valentin, for he 

 remarks the existence of " very large globules" 

 among the primitive fibres, similar to what he 

 and Purkinje had noticed in the grey matter of 

 the olfactory bulbs.* If this view of the peri- 

 pheral expansion of the auditory nerve be cor- 

 rect, its analogy with the optic is very obvious; 

 and it may be conjectured of the ear, as in 

 reference to the eye, that around a process from 

 the brain an apparatus has been organized fitted 

 to transmit and modify sonorous undulations. 



In the present state of observation we should 

 not be justified in making any positive state- 

 ment with reference to either the central or 

 peripheral connexions of the nerves, beyond the 

 following : that at the centres the grey and white 

 elements are always associated, and that nerves 

 may be truly said to arise out of grey matter ; and 

 that at the periphery, the nervous fibres, which 

 in their progress from centre to circumference 

 were bound together, become separated, and 

 connect themselves, probably by intimate ad- 

 hesion, with the elementary parts of the tissues 

 and organs to which they are distributed. 



Of the ganglionic nerves. Without more 

 exact information respecting the minute ana- 

 tomy of these nerves, our knowledge of the 

 peculiar function of the ganglionic system must 

 be very incomplete. The following questions 

 suggest themselves in reference to this system. 

 1. Are its anatomical characters sufficiently 

 distinct from those of the cerebro-spinal system 

 to warrant us in separating it from that system, 

 if only for purposes of description ? 2. Is it 

 an independent system, as some have conjec- 

 tured, giving fibres to the cerebro-spinal nerves 

 as well as receiving some from them. 3. If it 

 be an independent system, wherein consist the 

 peculiar features by which its fibres are to be dis- 

 tinguished from those of cerebro-spinal nerves ? 



There are many features belonging to this 

 system which justify its separation from that of 

 the brain and spinal cord. The great number 

 of ganglions connected with it, suggests the 

 propriety of designating it ganglionic system, 

 nor does the existence of ganglions on the pos- 

 terior roots of spinal nerves render this appella- 

 tion less proper; for in this system every nerve, 

 nay every fibre, is connected with or passes 

 through one or more ganglions. The external 

 aspect of these nerves is very characteristic. 

 Their neurilemma is very dense, and has more 

 of the silvery appearance of white fibrous tissue 

 than the sheaths of cerebro-spinal nerves ; they 

 want the fasciculated character of the latter 

 nerves, and their colour has a diffused greyish 

 or greyish red hue. The smaller ramifications 

 are exceedingly delicate and appear to be soft, 



* Valentin, liber den Verlauf und die letzen 

 Enden der Nerven, p. 63. 



