X PRACTICAL DIRECTIONS 539 



the outer margin of the iris, the choroid, and the ciliary vessels and 

 neivcs. Then make two radial cuts, a short distance from one another, 

 through the iris, and turn back tlie portion between the cuts, noting the 

 ciliary processes. Sketcli. 



Cut through tlie choroid and tlie parts enclosed by it, horizontally, 

 around the line up to which it has been already exposed, so as to 

 separate the eye-ball into an inner and outer hemisphere : in doing so, 

 the gelatinous vitreous humour must be cut with the scissors. Examine 

 and sketch both sections, noting in the outer hemisphere — the retina, 

 stopping short at the outer margin of the ciliary processes, and the lens 

 with its capsule ; and in the inner hemisphere — the retina with its blood- 

 vessels, and the blind-sfot (or point of entrance of the optic nerve). 

 Then remove the retina and observe the choroid with its iridescent 

 tapetuni. 



2. Cut your second specimen into vertical halves with the scissors, 

 making the cut pass through the cornea, pupil, and optic nerve. As it 

 is difficult to cut through the lens without disturbing its relations, it 

 should be carefully separated from one half, and left entire on the other 

 half. Examine the relations of the parts once more, compare Fig. 57, 

 and sketch. 



I- Dissection of typical flexor and extensor muscles and 

 joints of the fore-limb. 



1. Expose the biceps (chief ^exor of the fore-arm). Its origin is 

 from the anterior edge of the glenoid cavity on the pectoral arch : it 

 arises by a single long tendon, working in the bicipital groove of the 

 humerus. It is spindle-shaped, consisting of a single belly, and is 

 inserted on to the proximal end of the radius. 



2. Expose the triceps (chief extensor of the fore-arm). It arises 

 by three main heads from the pectoral arch and humerus, and is inserted 

 on to the olecranon process of the ulna. 



3. Remove the muscles from the shoulder-joint, and note the 

 capsular ligament (p. 55). Cut through this so as to open the synovial 

 capsule, and noVe. 'Cm synovial membrane axiiiiJltiidsxiA the cartilaginous 

 articular surfaces of the glenoid cavity and head of the humerus 

 respectively : or, prepare as directed on p. 64 in the case of the hip- 

 joint of the frog. 



4. As an example of a muscle with a multiple insertion, dissect out 

 the extensor communis digitorum (dorsal). It arises from the distal 



