THE ORGAN OF HEARING. 



The blood-vessels supplying the cochlea constitute two 

 groups, the branches distributed to the membranous cochlea 

 and the numerous twigs destined for the bony capsule. The 

 cochlear branch of the auditory artery, just before its passage 

 through the bony wall, divides into fifteen to twenty twigs, which 

 pass either directly through canals to supply the lowest turn of the 

 cochlea or into the modiolus. The vessels within the central canal 

 of the modiolus, after supplying the nerve-trunks and the spiral 

 ganglion with nutritive twigs, send off lateral branches, which form 

 two remarkable masses of coiled vessels, the glomeruli cochleae ; 

 from the larger of these, situated somewhat above the point of origin 

 of the bony spiral lamina, arterioles proceed to Reissner's membrane 

 and to the limbus, breaking up to form the capillary net-works of 

 these structures. The smaller glomeruli, within the base of the 

 partitions separating the adjoining cochlear turns, send off branches 

 forming two independent capillary systems. These are the net-works 

 within the basilar membrane and those of the stria vascularis, 

 which, while having a common origin, do not communicate. The 

 capillaries of the membranous cochlea are collected into two 

 principal trunks, the vas prominens on the outer wall and the vas 

 spirale beneath the basilar membrane opposite the inner rods of 

 Corti ; from these channels the blood is conveyed to the larger venous 

 trunk, the vena spiralis modioli, lying below the spiral ganglion 

 within the base of the osseous spiral lamina. 



The lymphatics of the internal ear are represented by the large 

 lymph-spaces included between the membranous labyrinth and 

 its bony capsule, the perilymphatic spaces of the semicircular 

 canals, the utricle, the saccule, and the cochlea. These large inter- 

 communicating spaces are in direct exchange with the subarach- 

 noidean and probably also the subdural intra-cranial lymph-cav- 

 ities. The demonstrated communication between the cavity of 

 the endolymph and the subdural space by means of the saccus 

 endolymphaticus brings the contents of the membranous labyrinth 

 into closer relations with the lymphatic system than was formerly 

 recognized. 



THE DEVELOPMENT OF THE EAR. 



The development of the ear includes the formation of two mor- 

 phologically distinct divisions, the membranous labyrinth, the 

 essential auditory structure, and the accessory parts, comprising 

 the middle ear, with its ossicles and associated cavities, and the 

 external auditory canal and the pinna. 



The developmental history of the organ of hearing proper in its 

 early stages is largely an account of the growth and differentiation 



