VASCULAR SYSTEM. 129 



Organization of the Vascular System with Black 

 Blood. 



Q. Of what is the peculiar membrane of the veins com- 

 posed? 



#. It is a fine layer of longitudinal fibres. 



Q. Where is this membrane most conspicuous? 



#. In those veins where gravity is the most operative; 

 and in the superficial veins where pressure does not aid 

 the circulation as in the deep-seated veins. These fibres 

 can be better seen in the branches than in the trunks. 



Q. What is Bichat's opinion of this membrane? 



#. That it is a texture sui generis. 



Q. What distinguishes it from the arterial coat? 



*&. The absence of elasticity and brittleness; its soft- 

 ness; its great extensibility of texture j and the longitudi- 

 nal direction of its fibres. There are no circular fibres in 

 the veins. 



Q. Where is this peculiar membrane found wanting? 



ft. In the sinuses of the dura mater there is neither the 

 cellular coat nor fibrous membrane; the venous coats there 

 are the dura mater and common lining venous membrane. 



Q. How does the common membrane of the black blood 

 system differ from that lining the arteries? 



#. It is more distensible, it is more delicate, it never 

 ossifies. Hence you do not see ossification in the right 

 side of the heart. 



Q. Where does Beclard say the venous valves are most < 

 numerous? 



<ft. In the superficial veins; in those of the inferior ex- 

 tremities. 



Q. In what part of the venous system are there no valves? 



#. There are none in the pulmonary veins, except just 

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