1376 



VEIN. 



trasting remarkably with that of the heart : 

 this exists in less amount in the immediate 

 vicinity of that organ. 



There is yet another peculiarity in the 

 structure of the great veins near the heart, 

 they have a partial investment of the serous 

 layer of the pericardium ; this, however, exists 

 only on the anterior surface ; and in the in- 

 ferior cava the amount of serous covering is 

 very small. 



Fig. 861. 



\\ 



A Mass of Muscular Fibres from the Middle, Coat 

 of the Superior Vena Cava of the Human Subject, 

 eight or ten lines above its junction with the Auricle. 

 (Magnified 200 diameters.) 



IT. When the caves pass through the peri- 

 cardium and diaphragm they contract an inti- 

 mate connection with those structures whose 

 fibrous tissue is more or less reflected upon 

 them and adds to their coats. Upon the su- 

 perior cava are to be seen (external to the 

 pericardium) white, glistening fibres, having a 

 longitudinal course, and traceable from the 

 pericardium directly upon the vein. The 

 pulmonary veins have a similar covering. 



In the human subject, the inferior cava 

 passes through the pericardium and diaphragm 

 at once, and there forms so intimate an ad- 

 hesion to the margin of the aperture that I 

 have removed striped muscle (of the dia- 

 phragm) from the fibrous tissue of the vessel, 

 it having taken its origin from the outer tunic 

 of the vein. 



In many of the lower animals (as in the 

 sheep, cat, and rabbit,} there is a considerable 

 interval between the diaphragm and pericar- 

 dium, in which the vena cava inferior is in- 

 vested with a covering of fibrous tissue con- 

 tributed from both these sources. It is white, 



glistening, and strictly longitudinal, and is fur- 

 nished in largest amount by the pericardium. 



III. Cerebral sinuses. The cerebral sinuses 

 hold the place of large veins to the brain, but 

 are materially different from large veins in 

 structure. They consist of excavations or 

 tubes in the substance of the dura mater, 

 the dura mater is, as it were, split into two 

 layers, and the interval is the cavity of the 

 sinus. Their form, which is very irregular 

 triangular, quadrilateral, &c. differs in dif- 

 ferent situations. 



The internal or lining membrane of the 

 sinuses is stated by all anatomists to be iden- 

 tical with that of the veins ; but its exact 

 amount and nature I have not myself ascer- 

 tained. The continuity of the lining mem- 

 brane with that of the veins is seen where 

 the sinuses join the veins ; thus, at the ca- 

 vernous sinus, where the ophthalmic vein and 

 circular sinus join it, the lining membrane 

 adheres to the inner wall of the sinus, but is 

 separated from the outer by the carotid artery 

 and certain nerves. The other element of the 

 walls of these peculiar veins is the white 

 fibrous tissue of the dura mater, arranged 

 without any regularity. The inner surface 

 of these vessels is smooth, but rendered ex- 

 tremely irregular by the occurrence of nu- 

 merous fibrous processes on bands projecting 

 into their cavity. In the superior longitudinal 

 sinus, the cavernous, and middle basilar, this is 

 most conspicuous. In the first mentioned 

 of these, the fibrous bands have been called 

 " cordcs WillisiancB " (after Willis, their first 

 describer). They are slips of white fibrous 

 tissue passing from the sides of the sinus, es- 

 pecially near the angles, attached at both 

 extremities, and either free or attached along 

 one side : these give the appearance as if the 

 inner surface were divided into cells ; into some 

 of these the probe enters and passes on into 

 the veins on the surface of the brain ; others are 

 blind, or lead to lesser sinuses, which not un- 

 frequently run parallel, for some length, to the 

 great sinus ; or the probe passes from one of 

 these cells to another. In the cavernous 

 sinus these fibrous bands are so numerous 

 that they look like a mass of areolar tissue, 

 whose areolae are distended with blood. The 

 cordae Willisianae are traversed by minute 

 arteries. (Sir C. #<//.) 



IV. The umbilical vein has a structure quite 

 peculiar to itself. The vessel may be b^st 

 examined by splitting it up with a director 

 and pinning it down on cork, with its inner 

 surface upwards. It is then seen to be smooth, 

 valveless, and whiter than other veins. 



From the inner surface I have obtained 

 epithelium : the cells were flat, irregular in 

 outline, granular and fatty. 



On making an incision, the membrane of 

 which it is composed retracts, so as to leave a 

 gap, and displays the dense fibrous mass which 

 forms the basis of the cord. It tears off in 

 irregular shreds, not showing a tendency to 

 tear in any particular direction. With care, 

 considerable portions of the membrane may 

 be stripped off. This structure is soft, elastic, 



