346 Dr. U. Pritchard on the [Mar. 2, 



I. " The Organ of Corti in Mammals." By Urban Pritchard, 



M.D., F.R.C.S., Lecturer on Physiology (Evening Classes), 

 King's College, London, Surgeon to the Royal Ear Dispen- 

 sary. Communicated by Prof. Huxley, Sec. U.S., LL.D., &c. 

 Received January 18, 1876. 



(Abstract.) 



I have divided my subject into three parts, namely, I. The Structure, 



II. The Innervation, III. The Development o£ the Organ of Corti, con- 

 cluding with a few remarks on its function, the mode of preparation 

 employed, and the nature of the animals examined. 



Part I. — The Structure of the Organ oe Corti. 



This apparatus, the essential portion of the cochlea, is situated partly 

 on the lower lip of the limbus, or terminal portion of the bony lamina 

 spiralis, and partly on the membrana basilaris ; on either side it is 

 bounded by epithelial cells, being itself developed from epithelium, as will 

 be shown hereafter. 



It consists of the following parts : — 



(1) The rods or fibres of Corti. 



(2) The ciliated or hair-cells. 



(3) Certain nuclear cells. 



(4) The supporting cells. 



(5) The membrana reticularis. 



(6) The membrana tectoria. 



(1) The Rods of Corti are arranged in two rows, an inner and an outer, 

 with their upper extremities in close contact, but separated by a consi- 

 derable interval below ; so that the two rows, sloping towards each other, 

 form the roof of a triangular tunnel. 



The rods stand almost in the centre of the organ, the foot of the inner 

 rod standing on the lower lip of the limbus, and that of the outer on the 

 membrana basilaris. On either side of the rods are situated the various 

 cells; above and closely adherent to them is the membrana reticularis, 

 and above this again lies the thick membrana tectoria. 



The form of the rods is similar to that of a long bone, consisting of a 

 cylindrical shaft with two enlarged extremities. The lower of these is 

 conical in both the outer and inner rods, but their upper extremities or 

 heads differ considerably in form. The head of the inner rod is somewhat 

 cuboid in form, compressed laterally ; and at its upper part it is prolonged 

 into a long slender process, which overlaps and covers the head of the 

 outer rod, this process being a direct prolongation of the upper surface. 

 The outer surface of this rod-head presents a concavity for articulation 



