PATTERNS OF THE A-V PATHWAYS 



9'5 



Burrage (67). The most likely explanation for inter- 

 mittent flow through these minute capillary vessels 

 is that the terminal arterioles and precapillary 

 vessels which supply the capillary nets exhibit spon- 

 taneous vasomotion as seen in other areas. 



Microcirculation in the Cochlea 



The general pattern of blood vessels of the cochlea 

 has been known for some time, the early descriptions 

 being obtained from injected and fixed material. 

 In general terms (40) the cochlea is supplied by the 

 cochlear artery. This vessel enters the modiolus 

 through the internal auditory meatus. The spiral 

 ganglion has a rich supply of capillaries, and many 

 arterioles find their way to the spiral ligament by way 

 of the roof of the scala vestibuli. The stria vascularis 

 is a rich network of small blood vessels with many 

 anastomotic connections. The limbus has a capillary 

 supply, and the tympanic surface of the basilar 

 membrane often has a small arteriole running along 

 it. Renewed interest in the blood supply of the 

 cochlea in the past few years has resulted from apply- 

 ing microcirculatory techniques to this rather in- 

 accessible site. 



The capillary networks of several portions of the 

 cochlea have been studied in detail. The areas so 

 studied include the spiral ligament, a projection of 

 thickened periosteum lying on the outer wall of the 

 osseous canal of the cochlea; the spiral prominence, 

 a slight ridge which projects into the cochlear duct; 

 and the stria vascularis, the part of the spiral ligament 

 lying on the outer wall of the cochlear duct between 

 the spiral prominence and the vestibular membrane. 



Two papers by Smith (1 10, 1 1 1), which contain a 



detailed description of cochlea blood vessels obtained 

 from fixed material, will be considered before dis- 

 cussing in vivo preparations. Investigations of 

 capillary beds following intravascular precipitation 

 of Prussian blue or lead chromate in the cochlea of 

 guinea pigs, cats, and humans were carried out by 

 Smith. She felt that while large features of the circu- 

 latory patterns had been adequately demonstrated, 

 the capillary beds had been indistinctly shown and 

 no attempts had been made to locate them precisely 

 in relation to various portions of the inner ear. 



In these studies, the radiating arteriole was found 

 to ramify into terminal branches before entering the 

 spiral ligament. In the cat and guinea pig four groups 

 of small vessels, depending on their location and the 

 course which they took, were designated by Smith. 

 The first group was the network of the upper spiral 

 ligament, group two was in the stria vascularis, group 

 three was found in the spiral prominence, while 

 group four was formed by the capillaries of the lower 

 portion of the spiral ligament. In human labyrinths 

 a fifth group, straight vessels in the thicker portion of 

 the spiral ligament, was included in the classification 

 (see fig. 18). The network in the upper spiral ligament 

 is described as follows: Small branches from the 

 radiating arteriole or one of its terminal ramifications 

 have a winding course in a spiral direction usually 

 above the attachment of Reissner's membrane. These 

 small branches are seen to anastomose with other 

 tributaries. They leave the upper spiral ligament bv 

 turning downward to the thicker part of the spiral 

 ligament where they join venules, or they may turn 

 upward and go through the bone wall to end in a 

 collecting vein. The capillaries in the second group, 

 the stria vascularis, are extensively connected with 



fig. 18. Schematic drawing showing typical 

 distribution of small blood vessels in the spiral 

 ligament of the human cochlea. [From Smith & 

 Giovacchine (113).] 



