320 



MANUAL OF HISTOLOGY. 



Fio. 147. Diagram illustrating tba 

 structure of the ependyma of the cere- 

 bral ventricles. 



of the cord, and doubtless like it in function, the cerebral ven- 

 tricles resemble it in their structure. They are lined through- 

 out with a structure called the ependyma. This consists first 

 of a finely granular layer covering all the nervous matter 

 bounding the ventricles. Besides the minute granules, this 



layer contains a few small nuclei here 

 and there, but no fibres. On its free 

 surface rests a single layer of cylin- 

 drical epithelium. The cells of this 

 layer have square free ends, while 

 they are anchored by one or more 

 delicate processes which emerge from 

 the attached end and pierce the sub- 

 jacent granular-matrix. These epi- 

 thelia in the fresh state undoubtedly have cilia. This layer 

 of epithelium is apt to be arranged in folds, giving a section 

 of the ependyma a wavy appearance. 



The chor old plexus of the lateral ventricles has for its basis 

 an artery which enters the descending horn of the lateral ven- 

 tricle from the base of the brain. This artery gives off along 

 its course short arterial trunks which repeatedly subdivide, and 

 each ultimate arteriole terminates in a convoluted capillary 

 loop, resembling the Malpighian tuft of the kidney. Some 

 of the twigs seem to end in a cse- 

 cal extremity ; but it is doubtful 

 whether they do, the preparations 

 giving this appearance being prob- 

 ably artificial. The peculiarity of 

 the choroid plexus is that all the 

 vessels composing it, large and 

 small, are covered by a layer of 

 polyhedral epithelial cells, each 

 having one, sometimes two large 

 nuclei. This presents a beautiful 

 example of the so-called tesselated 

 epithelium, each cell being sepa- 

 rated from its neighbor by a transparent intercellular sub- 

 stance. This epithelial covering causes the tufts of the choroid 

 plexus to resemble, in a degree, the villi of the chorion. The 

 best plan in studying the choroid plexus is to use hsema- 

 toxylon, or alcoholic specimens slightly teased. 



Fio. 148. Diagram showing structure 

 of the choroid plexus of the lateral ven- 

 tricles. 



