AND OF THE CAUDAL END OF THE SPINAL CORD. 1^3 



stage of nerve-fibers, especially those from the ventral portion of the spmal cord, 

 although von KoUiker does not hold this view. After the development of the ven- 

 triculus terminahs the caudal portion of the conus medullaris is converted into the 

 filum terminale by the ventriculus terminalis and conus medullaris moving cranial- 

 ward. This is due to the fact that the gray substance which Ues next to the ven- 

 triculus terminahs is undergoing degeneration and the caudal end of the central 

 canal is gradually excavated, while the caudal end of the ventriculus terminalis 

 narrows by degrees, losing its cellular substance. The relative lengthening of the 

 filum terminale, therefore, is due to the growth of the nerve-fibers with their sheath 

 of dura mater and pia mater, and in part also to the gradual addition of tissue 

 from the caudal portion of the conus medullaris, which has become converted into 

 the tissue of the filum terminale. 



ABNORMALITIES OF THE CAUDAL END OF THE SPINAL CORD. 

 (a) Embryo No. 40.5, 26 mm. ; (b) embryo No. 145, 33 mm. ; (c) embryo No. 449, 36 mm. 



In the first two specimens the caudal tip of the neural tube is spiral. It is 

 probable that this part is covered with a layer of epidermis, although I could not 

 discover it and therefore conclude that it was injured in the preparations. In 

 the first specimen the caudal end of the spinal cord enters into the tail-bud. Two 

 branches of the anterior spinal artery penetrate between the coils of the spinal 

 cord. In the second specimen the coil of the caudal end of the spinal cord forms 

 the summit of the papillary tail and terminates at the ventral side of its root. 

 The third specimen has only 32 vertebra? and no remnant of the neural tube. 



SPINAL GANGLIA. 



It is very difficult to locate the first cervical ganghon at a very early stage 

 of embryonic develoi)ment, particularly if the specimen is poorly preserved. This 

 structure is frequently found in close apposition to the Froriep ganghon on the 

 trunk of the spinal accessory nerve. Sometimes it is poorly developed and re- 

 sembles a Froriep ganglion, except for the fact that it hes always on the ventral 

 side of the trunk of the accessory nerve, while the Froriep ganglion lies on the 

 dorsal side. The first cervical is smaller than the others, and the second in turn 

 is smaller than the third. In embryo No. 991 (17 mm.) both first cervical ganglia 

 are lacking. In embryos from 5 to 10 mm. there are in most cases 32 pairs of 

 ganglia; from 12 to 14 mm. there may be 33 pairs. When the number is 33 the 

 last caudal ganghon is usually very small and has no nerve. In embryos from 15 

 to 33 mm. the number is usually 31. I have frequently found the thirty-second 

 spinal nerve without a ganglion, the latter having degenerated. In embryos from 

 35 to 67 nma. long, and older, there are usually only 30 ganglia; occasionally there 

 may be 31, but the last is usually undergoing degeneration. 



SYMPATHETIC GANGLIA. 



In embryos 33 mm. long, and older, the caudal ends of the paired sympathetic 

 ganglionated nerve-trunks join together at the upper plane of the ventral side of 

 the thirtieth vertebra, as shown in text-figure 2. At the point of union there is 



