1370 



VKIN. 



I have given it a different interpretation: I 

 have indeed considered it as a reduplication 

 of the fenestrated membrane, existing there in 

 a state of great tenuity and destitute of fibrous 

 striations. 



From the vena cava of the human subject 

 I have obtained epithelium, differing far from 

 the normal form. The specimen consisted 

 of flat, irregular cells, with a small bright 

 nucleus ; some cells distinct, others pale and 

 ill defined ; some densely granular, others 

 scarcely so at all. 



In Birds (Loon Colymbui septentrionalis), 

 I have seen the epithelium diamond-shaped, 

 with a large, flat, bright nucleus. 



In Batraclda (Frog Rana temporaria), 

 the epithelium was large, pale, and irregular. 



In Fish (Cod Gad us morrhua) the epi- 

 thelium was large, irregular, and granular. 



Fenestrated membrane. This structure, 

 which Henle has called the "fenestrated," or 

 " striated " membrane, is placed intermediately 

 between the epithelium and the Hiiro-vascular 

 elements of the vessels' walls, and, from this 

 circumstance, as well as its ph\Mcal proper- 

 ties, it bears a strong resemblance to the 

 basement or limitary membranes on the skin, 

 the serous and mucous surfaces. 



This structure has been described and 

 figured by Henle, in a manner which exactly 

 coincides with my own observations. When 

 a portion of the membrane is stripped off the 

 inner surface of a vein (or artery, for it is the 

 same in either), and examined under the 

 microscope, it is found to consist of a thin, 

 continuous sheet, of a pellucid, structureless 

 membrane, to which are adherent some re- 

 ticulated fibres, having a longitudinal direc- 

 tion hence it is " striated." It is also fre- 

 quently perforated with small holes, from 

 which circumstance it is called " fenestrated." 

 This homogeneous membrane has the remark- 

 able property of rolling itself up in the form 

 of a scroll, somewhat like the elastic laminae of 

 the cornea. According to Henle, it rolls 

 itself in the longitudinal direction, but I have 

 found the same tendency in the opposite 

 course. The apertures, or fenestrae, seen on 

 the membrane, all have more or less of a cir- 

 cular or oval form, and I have found that the 

 number and extent of these perforations de- 

 pend on the manipulation it has undergone. 

 Its physical properties are peculiar ; it is crisp 

 and somewhat elastic, and its inclination to roll 

 up in a scroll is so great, that it is never seen 

 in a flat form. The elasticity, which it pos- 

 sesses, is the reason, as it seems to me, why 

 the fenestrse are universally of a rounded 

 form ; for when any lesion is effected in it, 

 retraction occurs all round from the injury, 

 and thus makes the point or line of lesion the 

 axis of a circular or oval aperture, as the case 

 may be. In several specimens of this tissue, 

 in which no fenestras at first existed, I have 

 produced them to any extent by pricking or 

 lacerating it with needles. The fenestras in 

 the figure were thus produced. 



The longitudinal striations appear to me to 

 be some fibres of the next tunic, the in- 



ternal longitudinal fibrous coat accidentally 

 adherent to the homogeneous membrane.* 



Fi?. 854. 



Fenestrated or Striated Membrane from the Ju- 

 gular Vein of the Red-throated Diver (Colymbus 

 septentrionalis). 



a, Fenestrae. (Magnified about 100 diameters.) 



In the accompanying drawing (Jig. 854*.) is 

 represented a portion of this membrane, from 

 the jugular vein of the red-throated diver 

 (Colymbm septentrionalis). It was of a pale 

 pink tint, from contact with the blood in the 

 vessel, and, seen by transmitted light in the mi- 

 croscope, had a slight yellow cast. It was 

 marked by fine longitudinal threads on one 

 surface, which projected at some spots beyond 

 the torn edge of the membrane. 



Purkinje and Rauschel consider this mem- 

 brane as similar to the middle coat of arteries. 

 Valentin describes it as a peculiar structure- 

 less membrane. Henle considers it as a tran- 

 sition from epithelium to fibrous tissue, in 

 which opinion he is supported by Schwann. 



The fenestrated membrane has been found 

 on various parts of the internal surface of the 

 arteries and veins ; but the best specimens I 

 have seen have been from the principal veins 

 of large birds (goose, loon, gull), &c. At the 



* Henle has made a singular speculation concern- 

 ing the nature of this structure: he believes it to be 

 au intermediate stage between the epithelium and 

 the longitudinal fibres next beneath it that the 

 former is converted into the latter, and that this is 

 its intermediate condition. He believes that the 

 epithelium becomes fused into a continuous sheet, 

 and the nuclei absorbed, and that this subsequently 

 breaks up into ribres, in short, that fibrous tissue 

 is formed from epithelium, and that the coats of the 

 vessels derive their density and increase from the 

 epithelial cells secreted on their interior. 



