VEIN. 



1369 



This may be taken as a tabular view of the 

 typical structure of veins of larger size, and 

 in the smaller vessels the same order of parts 

 is represented, but with less distinctness and 

 greater tenuity. There are certain regions, 

 however, where the venous texture, both in 

 quality and order, departs considerably from 

 the typical arrangement : these will be noticed 

 hereafter. 



In the following observations, the several 

 coats of the veins will be described in succes- 

 sion, beginning with the innermost. 



Epithelium. It is difficult (as has been ob- 

 served by Henle}, in all cases, to make out a dis- 

 tinct epithelial layer lining the vascular cavity; 

 but, as far as my observations go, it is more 

 constant in arteries than in veins, and the 

 epithelium is more perfectly formed in the 

 former than in the latter. The anatomist will 

 frequently make search in vain for epithelium 

 on the inner surface of veins, and, when found, 

 a perfect epithelial cell is less common than 

 one imperfectly formed, the nucleus existing, 

 but the cell-wall either partially or wholly 

 absent. 



Fig. 853. 



Epithelium from the Vena Cava of a Sheep. 



a, perfect epithelium ; ft, common form ; c, epithe- 

 lium seen edgewise; cl, nuclei of epithelium desti- 

 tute of cell-wall. (Magnified 200 diameters.) 



The best method for examining the epithe- 

 lium is by scraping the inner surface of the 

 vessel, and placing the material removed on a 

 slip of glass; or by viewing the free edge of a 

 valve under the microscope. Existing in its 

 most perfect form the epithelium is of a dia- 

 mond or rhomboidal figure, containing a 

 nucleus, large in proportion to the cell, of a 

 pranulai character, and lenticular or oval form. 

 The nucleus is distinct and well defined. The 

 cell itself is clear, pale, and watery to an ex- 

 tent that it is impossible to portray in a wood- 

 cut. Henle states that the longaxis of the rhom- 

 boid corresponds with that of the vessel in 

 which it exists. In the figure ( /?.853.), is re- 

 presented the most perfectly (brined specimen 

 I have seen from a vein ; the rhomboidal figure 

 being very marked : it was obtained from the 

 vena cava of a sheep. There is also seen 

 . 853. &), a more common form, where the 



cell and nucleus are both present, but the 

 structure is less regular and more confused. 

 The epithelium is of the pavement or scaly 

 form, existing in a single layer : the cells are 

 flat, and either have no cavity, the opposed 

 sides being adherent, or the cavity is very 

 minute. This is displayed in the drawing 

 ( fig. 853. c), where some cells are seen edge- 

 wise : in this position the dimensions of the 

 nucleus are observed to bulge out the cell- 

 walls where it is placed, while the cell itself 

 forms a comparatively narrow line, or is even 

 reduced in appearance to a mere linear fila- 

 ment attached to the nucleus, sometimes at 

 one extremity and sometimes at both. 



But the condition in which I have most 

 commonly found the epithelium is that re- 

 presented at d in the accompanying figure ; 

 the nucleus, the essential part of the cell, 

 being apparently all that is present, and re- 

 presenting the whole epithelial structure. 

 These lenticular corpuscles, the nuclei, are 

 scattered on the inner surface of the vein in 

 pretty much the same position and form as if 

 the cells were present, but the cell-walls are 

 not sketched out, or the nuclei are only here 

 and there partially invested by a cell. This 

 appearance I have observed in the freshest 

 specimens, and it may also be produced by 

 keeping those where the cell is distinct for a 

 short time, when the cell-wall liquefies, and 

 becomes invisible. From the fact that the 

 nuclei are in some instances pretty equally 

 separated from each other, and hold about the 

 same relative distances, whether the cell-wall 

 be present or not, it would seem not impro- 

 bable that, where not visible, the cell might 

 still exist in a state of imperfect and indistinct 

 formation, that the blastema may be present 

 in a mucilaginous condition, but of sufficient 

 density to retain the nuclei in their proper 

 relative position. 



The nuclei may sometimes be seen thus 

 arranged on the surface of a valve near its 

 clear, thin edge, as is seen with unusual 

 distinctness in fig. 865. A. These appear- 

 ances are generally destroyed by manipulation. 

 When a valve is placed for examination, the 

 nuclei are apt to float off' its surface in the 

 fluid with which the object is moistened, and 

 arrange themselves along the free margin of 

 the valve in the interval between its edge and 

 the glasses. 



Henle has represented, in his matchless 

 work on general anatomy, the edge of a valve 

 magnified, in which the nuclei of epithelium 

 are arranged on a clear area, which rims the 

 margin of the valve; and this transparent, 

 structureless boundary he describes as the 

 epithelial cells, in which the nuclei, also 

 visible, are embedded. I have seen well de- 

 veloped epithelium at the edge of a valve, but 

 it did not present the appearance depicted by 

 Henle, the cell being a mere line as repre- 

 sented in^. 865. A. n, and scarcely forming a 

 transparent edge. I have also occasionally 

 seen a structureless rim to a valve, and as 

 that was not changed by the washing and 

 brushing off of the superimposed epithelium, 



