ally on the distal surface of the disc. The vertebral body is [99] 

 here proportionately thin, showing itself merely as a lighter 

 streak between the more deeply staining perichondrium of 

 each end. In fact the bodies of the distal coccygeal vertebrae 

 can hardly be spoken of as cartilaginous. In thickness (cranio- 

 caudal) the vertebral bodies diminish steadily throughout the 

 sacral and coccygeal regions, but there is very little diminu- 

 tion in the dorsoventral diameter until the thirty-fourth verte- 

 bra is reached. The last three diminish rapidly towards the 

 tip. In the last two the discs are fully as thick as the verte- 

 bral bodies themselves. The distal surface of the vertebra is 

 capped by a well marked disc. There is on each side of the 

 intervertebral discs in the coccygeal region a small mass of 

 deeply staining tissue, which projects ventrally and laterally. 

 They are visible only in sections which pass to the side of the 

 mid-line. They represent undoubtedly rudimentary hypa- 

 pophyses or haemal arches found in the caudal vertebrae of 

 lower forms. t 



The spinal ganglia, not counting the ganglion of the hypo- 

 glossus, are thirty-three in number. In connection with the 

 last a distinct ventral ramus arises and passes ventrally to 

 the side of the vertebrae, bending distally; ventral to the 

 vertebrae it joins a trunk from the next higher nerve. Its 

 mode of ending is uncertain. 



The number of muscle plates could not be made out clearly. 



In the interval between the thirty-first and thirty-second 

 vertebrae the medullary cord {med.) becomes suddenly attenu- 

 ated into a filum terminale. There are apparently few or no 

 neuroblasts beyond this point; the walls of the tube are made 

 up of columnar epithelial cells. In the distal portion of the 

 vertebral region and at the base of the caudal filament the 

 cord takes a somewhat sinuous course. The central canal 

 extends to the tip of the tail, where it ends in the slight 

 enlargment mentioned above, the terminal ventricle. 



The notochord (ch.) forms the axis of the vertebral bodies 

 and discs, and in the proximal portion of the coccygeal region, 

 as in the trunk, is almost straight. In the region of the last 

 two or three vertebrge it is more tortuous. It leaves the 



(11) 



