gi6 



HANDBOOK OF PHYSIOLOGY 



CIRCULATION II 



one another and give the appearance of a network 

 superimposed upon the deeper vessels of the spiral 

 ligament. The superior and inferior borders appear 

 straight and parallel. A large venule drains the 

 network, formed by the junction of three or four 

 strial capillaries. The venule turns backward and 

 leaves the stria vascularis in its lower half where it 

 descends peripherally, sometimes joined by other 

 venules before entering into the collecting venous 

 system at the lower edge of the spiral ligament. The 

 blood supply of the spiral prominence, the third 

 group, is different in the guinea pig from cat and man. 

 In the guinea pig a single vessel is found near the 

 epithelial layer, with perhaps a single layer of con- 

 nective tissue cells interposed. The vessel courses 

 parallel to the network of the stria vascularis just 

 below its inferior border, although no vessel of the 

 spiral prominence is ever connected to the network of 

 the stria vascularis. At times the vessel is double, with 

 the duplicate vessel running under the edge of the 

 stria vascularis. The venules join the collecting 

 venules of the lower spiral ligament. In the human, 

 the vessels in the spiral prominence form a separate, 

 narrow, rolled network below the stria vascularis, 

 supplied by large arteriolar vessels and drained by 

 large veins. Small vessels leave the network by turning 

 upward and laterally into the spiral ligament before 

 emptying into veins. They also may enter venules in 

 the lower spiral ligament. 



The capillary network in the lower spiral ligament 

 is also supplied by direct large arteriolar branches. 

 These arteriolar branches descend close behind the 

 stria vascularis and terminate in a spiral vessel in the 

 crest of the spiral ligament. Branches are given off 

 to the stria vascularis and spiral prominence on the 

 way. The spiral vessel marks the upper limit of a 

 network which originates from it. Where the spiral 

 ligament is quite thin, the network can be seen as a 

 loose mesh of vessels under the mesothelium of the 

 scala tympani. 



The fifth group found in the human is made up of 

 straight vessels found in the connective tissue between 

 the scalae and the bone. They show variations in size 

 and structure, and course directly from arteriole to 

 venule. Some seem to be capillaries, being devoid of 

 perivascular cells, while others are larger and may 

 represent a type of arteriovenous shunt. 



The radiating arteriole was found to have both 

 longitudinal and tangential smooth muscle cells and 

 a thin adventitia of two or three layers of connective 

 tissue cells. Capillaries were composed of endothelial 

 cells and infrequent smooth muscle cells. The capil- 



laries of the stria vascularis were composed only of 

 endothelial cells, although occasionally a perivascular 

 cell was seen. It could not be determined whether it 

 was a smooth muscle cell or not. The large draining 

 vein was seen to have a few smooth muscle cells 

 arranged transversely or tangentially. 



Smith concludes that the human cochlea shows a 

 definite arteriolar supply to the various vascular 

 groups of the spiral ligament. There are several 

 distinct capillary networks rather than one large 

 continuous field, and these networks are separated by 

 their vascular supply and drainage. She suggests that 

 such a vascular pattern makes it possible to have 

 regional circulatory variations within a small segment 

 of the spiral ligament. 



In 1954, Weille et al. (131, 132) published two 

 papers describing the circulation in the spiral liga- 

 ment and stria vascularis of the living guinea pig. 

 The cochlea was first exposed and then microscopic 

 fenestration of either the apical or third cochlear turn 

 was carried out. The vessels observed included 

 arterioles, arteriovenous anastomoses, capillaries, 

 and venules of the spiral ligament and the capillary 

 network of the stria vascularis. Capillaries of the 

 spiral ligament formed an intricate network of 

 dividing and anastomosing vessels fed by arterioles. 

 Arteriovenous anastomoses were formed as a branch 

 of an arteriole that entered a venule with no inter- 

 vening capillary network. The capillaries of the stria 

 vascularis formed a network of branching and 

 anastomosing vessels that emptied into the venules of 

 the spiral ligament. 



All arterioles, arteriovenous anastomoses, and 

 venules contracted and dilated independently. The 

 rate of blood flow varied in each vessel from time to 

 time, going from very rapid to no flow at all. 



A more detailed description followed (65), in which 

 it was reported that there were two distinct types of 

 tiny vessels, one in the area of the upper spiral liga- 

 ment and the other in the area of the pigmented 

 cells (the cochlear duct). Branching and anastomosing 

 were frequent in these networks. Both received blood 

 from the arterioles and both drained into the venules 

 in the area of the cochlear duct. 



Collecting venules, into which the capillaries drain, 

 pass transversely through the area of the cochlear 

 duct, and drain into the venules which are perpen- 

 dicular to them and lie outside this area. 



Vessels which ran from arterioles to venules were 

 seen to give off capillaries, but no capillaries were 

 seen to re-enter them. For this reason they were 

 called arteriovenous anastomoses rather than met- 



