46 ON THE NERVOUS SYSTEM IT. 



demonstrated, lying upon the sides of tlie vertebral column ; they are situated near 

 those small white vesicles, which protrude by becoming swollen, chiefly during 

 the spring of the year, and contain numerous microscopic calcareous crystals." * 

 Stannius describes them as an accumulation of the white substance which covers 

 the pia mater around the nerves where they escape from the spinal canal, and 

 which, under the microscope, has the appearance of a mass of crystals, f Professor 

 Owen has usually called attention to them in his annual Hunterian lectures, though 

 he has published nothing in relation to them. 



As I have seen them in dissections, they are subject to some variety, but exist on 

 the trunks of all the true spinal nerves, the hypoglossus included, and invest them 

 more or less completely at their exit from the spinal canal, occupying the space be- 

 tween the transverse processes of two adjoining vertebrae. The capsule is a very 

 thin membrane, sometimes having a diameter of two or three lines ; its surface is 

 minutely lobulated, an appearance which results from the existence of numerous 

 partitions within, forming many small cavities, which communicate, though not 

 very freely, with each other. The contents of these pouches are vast numbers of 

 exceedingly minute crystals of a somewhat oval form (Plate I. Fig. 18), pointed 

 at their extremities, and comparable in shape to a lemon-seed, but sometimes pre- 

 senting well-defined angles. 



These capsules are not in any definite proportion to the size of the nerves to 

 which they are attached, those of the brachial, for example, which is one of the 

 largest pairs of nerves, being much smaller than those connected with the dorsal 

 nerves, which are of less size. As to the statement by Wagner, that they are 

 found more swollen in the spring, this condition has not been noticed in the in- 

 stances which have fallen under my observation. I have detected them of nearly 

 equal dimensions at all seasons of the year, whether examined in spring, summer, 

 late in the autumn, or even in midwinter. They do not belong exclusively to the 

 adult period, but, as stated by Stannius, I have found them in the larvae at difterent 

 periods, even before the development of amis and legs. Dissections of other than 

 Raniform Batrachians have not led to their detection ; I have not found them in 

 Siren, Menohranchus, Bufo, or Salamandra, but have seen them in Rana fontinalis, 

 R. halecina, and R. pahtstris. They seem to be in these species constant appen- 

 dages to the spinal nerves. The crystals which these capsules include are similar in 

 size and form to those contained in the vestibule of the ear ; in the latter case they 

 are in contact with the extremity of the nerve, but in the former they are simply 

 attached to its sheath. 



Section VII. — Sympathetic Nerve. 



The small number to which pairs of spinal nerves are reduced involves, as a mat- 

 ter of course, a sympathetic nerve of a corresponding degree of simplicity. It is 

 connected with all of the nerves from the trigeminus to the third lumbar nerve in- 



* Comp. Anat. Verteb., Part. I. p. 151. + Manuel d'Anat. Comp., Tom. II. p. 200. 



