348 DISCOVERY REPORTS 



the ribs from the ist cervical to the 6th dorsal vertebra. They pass up between the 

 transverse processes into the neural canal. 



Two large thin-walled venous sinuses accompany the spinal chord as far forward as 

 the 7th cervical vertebra. Anterior to this the canal is filled with a venous plexus 

 extending into the skull through the foramen magnum and embracing the back of the 

 brain. 



From the neural venous sinuses intervertebral (descending intraspinous) veins descend 

 throughout the whole length of the body. In the neck region they are found also 

 collecting themselves from the venous plexuses in the neural canal. As far back as the 

 8th dorsal vertebra the intraspinous veins join the posterior thoracic. Posterior to the 

 8th dorsal vertebra they join the small azygos veins which have been shown to exist. 

 In the abdominal region they drain into the postcava. 



The precaval and postcaval venous systems are thus in free communication with one 

 another through the neural canal, and blood reaches the heart from the neural venous 

 sinuses in whichever direction it flows in them. Appearances suggest that these sinuses 

 are blood reservoirs. 



The rete surrounds all the descending intraspinous veins back to the 6th dorsal 

 vertebra. It surrounds them throughout the whole of their course and is in free com- 

 munication with them by means of numerous subsidiary twigs. The rete surrounds the 

 posterior thoracic vein and artery in the proximal parts of their course and also the roots 

 of the arteries ascending to the dorsal musculature from the posterior thoracic. 



The rete is everywhere in free communication with the vessels it surrounds, whether 

 arteries or veins. It does not, however, block the course of any of them. This is opposed 

 to the earlier conceptions of the retia, according to which these networks were supposed 

 to be formed on the course of either an artery or a vein. The foregoing description 

 shows that they must be looked upon as capillary systems intervening between arteries 

 and veins. 



The rete is in intimate contact with the muscles of the ist and 2nd intercostal spaces. 

 The blood supply to the intercostal muscles becomes increasingly generous proceeding 

 forwards. 



The rete is mainly under the control of the sympathetic nervous system but to some 

 extent of the somatic as well. 



THE BASICRANIAL RETE 



The cavity between the tympanic bulla and the articulation of the mandible is 

 occupied by a vascular network similar in appearance to the thoracic rete already 

 described, i.e. consisting of intimately related arteries and veins. 



RELATION TO SKULL 



The shape of the skull and the form of the basis cranii are extremely different in 

 foetus and adult. The position and relations of the basicranial rete were only examined 

 in detail in the foetus. From a general inspection of the adult basis cranii, however, it 



