432 Mr. Lawson Tait on the 



could. It extends from the omphalic ring at least 12 millims. up into 

 the true substance of the cord, giving off at short intervals thick trunks 

 which rapidly break up into capillaries. Nowhere in this peculiar vas- 

 cular arrangement of the cord, either central or superficial, have I seen 

 the capillaries turn up in loops as if to go back. They open, as I have 

 seen in innumerable instances, directly into the canalicular system ; and 

 it is possible to inject a large extent of all these districts of the sub- 

 stance of the cord by placing a nozzle in the vein and first injecting the 

 foetus. After that has been accomplished, the capillaries, and finally the 

 canalicular tissue of the cord, can be seen filling. In one section (Plate 

 13. fig. 15) the capillaries were seen opening into a limited district of the 

 canalicular tissue, which evidently was somewhere near the apex of its 

 cone. 



The injected tissue was in immediate relation to the walls of an 

 artery and of a vein. I believe that under favourable circumstances I 

 may yet succeed in this way in injecting the whole substance of the 

 cord. 



The point of origin of this sinus I have as yet failed to work out ; but 

 I conclude it comes from the intercosto-lumbar arteries, as the injection 

 of the cord does not appear until the skin of the abdomen is perfectly 

 blue. 



The superficial layer of capillaries may also be seen entering the cana- 

 licular tissue of the cord. They lie immediately under the surface of 

 the cord. 



It is quite evident that the analogy between this capillary supply for 

 the cord and the Haversian system of canals in bone is complete. The 

 Haversian canals admit red corpuscles, but the stellate lacunae admit 

 only liquor sanguinis. So it is with this nutrient arrangement of the 

 cord ; and not only is the function of the stellate canals of the cord 

 identical with that of the lacunae and canaliculi of bone, but their 

 anatomy is the same minus the deposit of the salts of lime which occupy 

 the alveoli. In the cord the place of the salts of lime is occupied by 

 water containing some organic compounds. 



In one cord I found a capillary extending nearly an inch from the 

 omphalic structures, and which, when its surrounding and concentric 

 layers of nucleated canals were stained with hsematoxylin, very closely 

 resembled an Haversian system (Plate 13. fig. 16). This is probably the 

 continuation of the central sinus, as it does not appear to have a definite 

 wall, and it lay about the middle of the section. 



As yet I have not been able to demonstrate this vascular mechanism 

 in any but perfectly fresh and mature children, because the friction to 

 be overcome in order to make the injection pass round the front walls of 

 the abdomen is so great that it requires a greater pressure than the 

 liver will stand in immature children, which generally have been dead 

 EOme time before they are injected. 



