GENERAL PHYSIOLOGY OF THE EPITHELIUMS. 201 



undecided. But, before being absolutely sure that these are 

 lymphatic vessels, we must follow them from their origin, 

 which is known, to the efferent trunks which they form at 

 their junction; and decide the course of these latter, up to 

 their ganglionic termination, as has been done with the 

 other parts of the lymphatic system." (Ch. Robin.) 1 This 

 gap has not yet been filled, and the ancient descriptions of 

 efferent lymphatic vessels of the brain are scarcely demon- 

 strative : Fohmann and Arnold made injections only of the 

 sub-arachnoid cellular tissue ; Mascagni appears to have ob- 

 tained more positive results (by means of the injection of 

 the arteries with the gelatine, and by the transudation of this 

 substance), but he could point out neither the beginning nor 

 end of the vessels which he has described. No one has been 

 able to discover these vessels since ; and their existence, 

 therefore, seems very doubtful (Sappey). 



The uncertainty of our knowledge becomes still more 

 striking as we approach the question of the structure of the 

 lymphatic capillaries which compose the original network: 

 the most contradictory opinions have been expressed as to 

 the origin of the lymphatic vessels and their close connection 

 with the surrounding tissues, but we can only review them 

 rapidly. 



1. The origins of the lymphatic vessels are formed fry the 

 capillary spaces, previously described, or by prolongations 

 in cul-de-sac, similar to the aforesaid capillaries, penetrating 

 the intestinal villosities (central chyliferi, or chyle-ducts), 

 the papilla3 of the tongue, etc. This view, which was that 

 of Mascagni, Panizza, and Cruveilhier, is now corroborated 

 principally by the researches of Sappey and Robin. The 

 coat of these capillaries is simply a layer of epithelial cells, 

 though some varicosities or other irregularities may be ob- 

 served ; which, in the thickness of certain organs, give them 

 a more or less indented or triangular shape (and might lead 

 to the belief that they are connected by extremely fine links 

 to the neighboring elements) ; it is only in the large capil- 

 laries near the efferent vessels, that we find in addition to 

 the epithelial layer (endothelium) annular fibres, and a hya- 

 line membrane studded with nuclei. 



The lymphatic capillaries, like the blood capillaries, thus 

 form everywhere a close network, separated from the other 



1 Robin, article Lympliatlques ; " Dictionnaire Encyclopediquo 

 des Sciences Medicales." 1870. 



