434: ABSORPTION. 



exceed them in diameter by from jaVo- to T 7 of an inch 

 These investing vessels follow the blood-vessels in their rami 

 fications, and contain a clear fluid, with bodies resembling 

 the lymph-corpuscles. When Robin first described these ves- 

 sels minutely, he did not state definitely their physiological 

 relations ; * but he has just published a memoir in which he 

 describes them as true lymphatic vessels, analogous to the 

 lymphatics which partly surround the small blood-ves- 

 sels in fishes, reptiles, and batrachians. 2 In these animals, 

 the lymphatics in many parts nearly surround the blood 

 vessels, to the walls of which the edges of their proper coat 

 are adherent ; and that portion of the wall of the blood- 

 vessel which is thus enclosed forms at the same time the wall 

 of the lymphatic. 3 This disposition of the lymphatics in the 

 brain and spinal cord would allow of free interchange by 

 endosmosis and exosmosis of the liquid portions of the blood 

 and the lymph. 



The following are the principal situations, in addition to 

 those already mentioned, in which lymphatic vessels have 

 never been satisfactorily demonstrated, and in which their 

 existence, even, is doubtful : the walls of the blood-vessels : 

 the osseous system; tendons, ligaments, and the general 

 fibrous system. It is almost unnecessary to add that they 

 are not found in the teeth, hair, nails, epidermis, and the 

 epithelial structures. 



The lymphatic vessels from the superficial and deep por- 

 tions of the head and face on the right side, and those from 



1 ROBIN, Recherches sur quelques Particularity de la Structure des Capillaires 

 de VEncephale. Journal de la Physiologic, Paris, 1859, tome ii., p. 543 et seq. 



2 ROBIN, Memoire sur V Anatomic des Lymphatiqucs des Torpilles. Journal 

 de I 1 Anatomic etde Physiologic, Paris, 1867, tome iv., p. 3 et seq. 



3 The essential anatomical characters of the canals surrounding the blood- 

 vessels in the nervous centres were described by His, in 1865, probably without 

 a knowledge of the previous observations of Robin. (His, On the Existence of a 

 Perivascular Canal-System in the Central Organs of the Nervous System, and 

 upon its relations to the Lymphatic System. British and Foreign Medico- Chirur- 

 gical Review, January, 1867, p. 237.) 



