*590 ^ MANUAL OF ANATOMY 



will afford the dissector a general knowledge of the component parts of the 

 eyeball. 



Upon another ox's eyeball the sclerotic and cornea are to be examined. 

 The sclerotic is to be carefully opened at a point in the course of the 

 equator down to the level of the chocolate-coloured choroid. Thereafter the 

 sclerotic is to be clipped completely round the eyeball in the course of the 

 equator, which will divide it into two parts — anterior and posterior. These 

 two parts are then to be carefully reflected, one forwards and the other 

 backwards, which may be facilitated by clipping each into flaps. The dark 

 brown tint of the inner surface of the sclerotic is to be noted, this being due 

 to the connective-tissue layer, called the lamina fusca. Processes passing from 

 the lamina fusca to the subjacent choroid coat will have been observed, these 

 processes traversing the perichoroidal lymph-space. 



The sclerotic having been removed in the foregoing manner, the dissector will 

 now obtain a view of the choroid or vascular coat, easily recognised by its 

 chocolate colour. If the dissector can succeed in washing out the pigment 

 from the choroid, he may obtain a view of the closely-set, whorled venae 

 vorticosae, which converge to four points, and form four vessels. These vessels 

 will then present a white appearance. 



Ciliary Process. — Upon another ox's eyeball a vertical-transverse section 

 is to be made, anterior to the line of the equator. The posterior segment is 

 to be laid aside in the meantime, for the examination of the posterior half of 

 the retina. The vitreous body having been removed from the anterior segment, 

 a good view will be obtained, from behind, of the ciliary processes, which radiate 

 from the periphery of the crystalline lens. 



Iris. — To obtain a view of the iris, and also of the ciliary processes, from 

 before, the cornea is to be clipped in another eyeball around the corneo-scleral 

 junction, and removed. This opens up the anterior part of the aqueous 

 chamber, and the iris can now be examined. The shape of the pupil in the 

 ox's eye is to be noted, it being much elongated in the transverse direc- 

 tion. 



Flaps of the anterior part of the sclerotic are then to be made with the scissors, 

 by clipping from before backwards, and thereafter they are to be turned 

 backwards. This may enable the dissector to obtain some knowledge of the 

 ciliary muscle, which may be recognised as a white ring in the region of the 

 corneo-scleral junction. In front of the ciliary muscle is the canal of Schlemm. 

 To demonstrate the canal of Petit a blow-pipe may be introduced, close to 

 the periphery of the crystalline lens, through the posterior layer of the zonula 

 of Zinn, behind the ciliary processes (see the text). By blowing air in, the 

 canal of Petit may become evident, and it may then present a sacculated 

 appearance. The suspensory ligament of the lens will be recognised as lying 

 in front of the canal of Petit. 



Crystalline Lens. — The iris having been removed, the anterior wall of the 

 capsule of the crystalline lens is to be laid open, when the lens will escape. The 

 outer portion of the lens will be felt to be soft, but the central portion, which 

 constitutes the nucleus, is of firm consistence. 



The posterior segment of the eyeball, recently laid aside, is now to be 

 examined by carefully removing the vitreous body. This will enable the 

 dissector to examine the posterior part of the retina from the front. 



The foregoing dissections having been made upon the ox's eyeballs, the 

 dissector should avail himself of the first opportunity of repeating them upon 

 the human eyeball. For this purpose the eye of a child will suffice, or a 

 human eye may possibly be obtained from the post-mortem room of a 

 hospital. 



1716 Spinal Cord. — To expose the spinal cord within the spinal canal, the 

 vertebral and sacral grooves of the vertebral column are to be cleaned as well 

 as possible by scraping away the muscles which occupy them. The laminas of 

 the vertebrae, having been thereby exposed, are to be sawn through on either 

 side in an inwardly slanting direction, and the ligamenta subflava, which 

 connect the laminae, are to be divided. The chisel and mallet should also 

 be used in this dissection. This will enable the dissector to remove the 

 posterior wall of the spinal canal, which will be available for the dissection 



