THE LYMPHATICS OF THE HEAD. 



949 



they communicate with the subarachnoid spaces. The third group of spaces is 

 formed by the subdural and subarachnoid spaces, but no special description need here 

 be given of these, since they are more properly described (page 1197) as portions of 

 the meninges than as parts of the lymphatic system. By some authors an epidiiral 

 space, situated between the dura and the skull, is also recognized. 



Lymph-spaces have been described as occurring in the substance of both the dura 

 and the pia, forming in the latter a rather close net-work with which the perivascular 

 spaces communicate. The spaces of both membranes communicate with the subdural 

 space, and those of the dura are said also to communicate with the epidural space. 

 Practically nothing is yet known concerning the lymphatics of the spinal cord. 

 The Eye and Orbit, — No lymphatic vessels have as yet been described as 

 occurring in the orbital tissues, nor do they occur in the eyeball. But, on the other 

 hand, numerous lymph-spaces occur in connection with the latter structure, one of 

 the most important of these being the space of Tenon (spatium interfasciale), with 

 which the remaining spaces communicate more or less directly (Fig. 800). A 

 description of this space has already been given (page 504), but it may be recalled 

 that, in the first place, the space is continued, by means of the supravaginal lymph- 



FlG. 800. 



Conjunctival sac 

 Space of Tenon 



Diagram showing relation of space of Tenon to intracranial lymph-spaces. 



path surrounding the optic nerve, along the latter to the apex of the orbit, where 

 it communicates with the subdural space of the cranium, injection of that space 

 resulting in the injection of the space of Tenon (Schwalbe), and, secondly, that the 

 sheaths of the anterior portions of the orbital muscles are formed by reflections of the 

 capsule of Tenon, so that no obstacles exist in the way of the passage of lymph 

 from the muscles into the space. 



The cavities occupied by the vitreous and aqueous humors have also been re- 

 garded as lymph-spaces, and pericellular spaces in the cornea, which come into rela- 

 tion with the lymphatic vessels of the conjunctiva at the corneal margin, are readily 

 demonstrable. In the tissue of the sclerotic spaces also occur, communicating on 

 the one hand with the space of Tenon and on the other with suprachoroid spaces 

 which are abundantly present in the lamina fusca of the choroid coat and, by means 

 of spaces accompanying the venae vorticosce, communicate with the space of Tenon. 



In the eyelids, conjunctiva, and lachrymal apparatus true lymphatic vessels occur. 

 In the eyelids three net-works have been distinguished, one of which is subcutaneous, 

 the second lies immediately external to the tarsal plate, and the third is subconjunctival. 

 Communicating branches pass between adjacent plexuses, especially between the 



