HEAD AND ANTERIOR CERVICAL STRUCTURES. 47 



Membranous Labyrinth Within the Vestibule: 



Saccule. Canalis reuniens. 

 Within each semicircular canal. 

 Structure: Tunica propria. 



Fibrous investment. 

 Epithelial lining. 

 Within the cochlea: 

 Membrana basilaris. 

 Membrane of Reissner. 



Ductus cochlearis, or membranous canal of the cochlea. 



Canalis reuniens. 

 Auditory nerve : 



Superior division : 



To utricle, superior and external semicircular canals. 

 Inferior division : 



To cochlea, saccule, posterior semicircular canal. 

 Vessels : 



Artery : Internal auditory branch : 



To vestibule and cochlea, with their membranous con- 

 tents. 

 Veins. 

 With a small chisel chip away the bone and expose the canal for the facial nerve. 



Facial nerve, 807-8. (7889) 



"At its superficial origin." Geniculate ganglion. 

 Branches, (i) : 



Great superficial petrosal nerve. 



Lesser superficial nerve. 



External superficial petrosal. 



Nerve to the stapedius. 



Chordi tympani. 



Communicating twig to the pneumogastric. 



Dissection of the Eyeball. 



For the dissection of the eyeball, procure several eyes of the pig, sheep, or ox. The eye of the pig most 

 closely resembles the human eye in form and structure, but on account of its size the eye of the ox is 

 more readily dissected. The conjunctiva, ocular muscles, and fat should be carefully removed, exposing 

 the eyeball ; in removing these, note the vena vorticosae issuing from the sclerotic, a little posterior to 

 the equator of the eyeball ; and near the optic nerve, the ciliary vessels and nerves entering the eyeball 

 through the sclerotic. 



To obtain a general idea of the arrangement of the parts composing the eyeball and for reference 

 during the dissection, make a series of sections of the eyeball ; to do this put a couple of eyes in small 

 tin boxes and place in a mixture of salt and crushed ice for three or four hours till frozen solid. With 

 a fine saw divide one of the eyes into an anterior and a posterior section, cutting it at the equator of the 

 eyeball ; divide the other eye into two lateral halves by an antero- posterior section, cut one of these 

 halves into a number of thin sections. Pin the sections in a tray and cover with water ; they can then 

 be examined to advantage with a glass. 



General structure of the eyeball. 



On examination of the sections it will be seen that the eyeball consists of tunics and 

 of refracting media or humors : 



The tunics forming the coats of the eyeball are : 



1. Tlie sclerotic and cornea. 



2. The choroidy ciliary processes and iris, 

 j. The retina. 



The refracting media or humors are : 

 /. The vitreous humor. 

 2. The crystalline lens and capsule, 

 j. The aqueous humor. 



Divide an eye at the equator of the eyeball and note the parts seen in each hemisphere. 



i. Posterior hemisphere, 880. (860) 



Retina. Retinal pigment layer. Membrana suprachoroidea. 



