150 
HISTOLOGY OF ANIMALS. 
Articular cartilage in the foetal condition is sup- 
plied with blood-vessels, which pass into its substance, 
and all parts in the neighbourhood of its articular 
surface are nourished by the vessels of the synovial 
membrane, which, as will be presently shown, always 
terminate in looped extremities immediately on the 
margin of the surface subjected to pressure. The glenoid 
cavity of a human foetus, Fig. 117, A, is surrounded by 
a margin of capillaries which project inwards as far as 
the socket for the reception of the head of the humerus, 
where each terminates in a looped extremity, the loop 
itself, Fig. 117, b, being sometimes dilated to two or 
three times the size of that of the vessel from which it 
is derived, it would seem that the synovial fluid is poured 
out from these dilated vascular loops. In a vertical 
section of the head of a metacarpal bone of an adult, 
the looped vessels of the synovial membrane are dis- 
tinctly seen passing upon the articular cartilage as far 
as the part subjected to friction ; these vessels do not 
enter the cartilage, neither is there any other source from 
which adult cartilage can derive its nutrition, except 
these vessels of the synovial membrane 
