DISTRIBUTION OF NON-MEDULLATED NERVE-FIBRES. 127 



spinal cord. The wall of this duct consists of the following 

 parts : 



a. A pale epithelium, occupying about two thirds of the 

 thickness of the wall, consisting of an internal superficial 

 layer, turned towards the lumen of the duct, of pale, thin, 

 conical, cylindrical cells, and a deeper layer of smaller, appa- 

 rently round cells, in which there is often only a very narrow 

 zone of protoplasm surrounding the relatively large nucleus. 

 The cells of the superficial layer are all provided with 

 bundles of cilia, which I have seen continue in lively motion 

 for more than three hours in specimens examined in fresh 

 serum. 



h. The membrana propria, next to the epithelium, con- 

 sists of connective tissue with numerous elastic fibres. 



c. Most externally is a loose adventitia, in which is a 

 network of remarkably large, richly branched pigment-cells, 

 and which contains the large blood-vessels and lymphatics. 



The capillary blood-vessels form a network with elongated 

 meshes, in the propria immediately under the epithelium. 

 Near the duct run large nerve-trunks of medullated fibres, 

 which are connected at the root of the tail by smaller 

 branches, and are provided with remarkably distinct ganglia, 

 (ganglia coccygea, vid. Krause 'Anatoraie des Kaninchens'). 

 The ganglionic cells of these latter are mostly unipolar, their 

 processes becoming surrounded by a medullary sheath imme- 

 diately after their origin. The ganglionic cells are mostly 

 each furnished with a capsule, but occasionally we find two, 

 three, or four, enclosed in a common capsule. 



I believe that I have also recognised spiral fibres. 



In their further course the nerve-trunks wind spirally 

 around the duct, contain hei'e and there small ganglionic 

 enlargements, and give ofi" numerous small branches, con- 

 sisting of only a few medullated fibres ; these last lie loosely 

 side by side in their sheath, and enter the propria. Here 

 they separate from each other and for a short distance have 

 a course parallel to the longitudinal axis ; they show here 

 and there swellings and varicosities of the medulla, giving 

 them the appearance of varicose fibres. They divide freely, 

 the thin branches being still always furnished with a dark 

 border. 



Finally, these last divide into several thin pale fibrils, the 

 medulla having just previously ceased quite suddenly. 



Of these last pale fibres some are in connection with large 

 cells which lie immediately under the epithelium, and possess 

 a relatively large vesicular nucleus, in which is a shining 

 nucleolus, resembling perfectly the nuclei of those ganglionic 



