74 E VOL UTION AND DISEASE. 



tooth ; this produces severe constitutional disturbance 

 which may place life in jeopardy. 



When dealing with the intestinal origin of the spinal 

 cord it was mentioned that the central canal of the cord 

 and the gut communicated with each other around the 

 caudal end of the notochord. This connecting passage 

 is known as the neurenteric canal, and the section of the 

 bowel into which it opens is known as the post-anal gut, 

 because it is situated posterior to the permanent outlet 

 of the bowel. In the elasmobranchs this section of the 

 primitive gut equals a third of its total length. The 

 coccygeal region is often the seat of congenital 

 tumours, some of which present peculiar characters. 

 The examples most interesting to us attain a very large 

 size often more than a kilogram in weight and are 

 situated anteriorly to the coccyx. Structurally they are 

 composed of cysts lined with epithelium, the stroma 

 consists of very young connective-tissue : sometimes 

 these tumours contain a portion of bowel lined with 

 mucous membrane, possessing Lieberkiihn's follicles 

 and Peyer's patches. 



A study of the development, structure, and relations 

 of the tumours will serve to convince any impartial 

 observer that they arise in connection with the post- 

 anal gut ; they are by no means rare ; few pathological 

 museums of any pretensions are without a specimen, 

 or a model of them, and all surgeons of experience 

 have encountered one or more examples of them. The 

 large specimens are incompatible with life, but smaller 

 ones have been successfully dealt with surgically. 

 Finally every gradation has been recorded, from per- 



