xi PRACTICAL DIRECTIONS 557 



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 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 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 note the synovial membrane 

 and fluid and 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 end of the humerus, and at the distal 

 end of the fore-arm divides into four tendons, which pass 

 through the annular ligament to digits 2-5 and are inserted 

 on the middle and distal phalanges. Note the sesamoid 

 bones on the palmar side of the joints of the digits. 



/. Side Dissection. 



Obtain another rabbit, and make a dissection from the side 

 (compare Fig. 135) as directed in the case of the dogfish and 

 frog (p. 480). Make out the structure and relations of all 

 the principal organs once more, and sketch your dissection. 



K. Transverse sections. 



The examination of transverse sections is most easily 

 and satisfactorily done by preparing microscopical sections 

 of a foetus not more than a couple of inches in length, as 

 directed in the case of the young dogfish (p. 480) : a fcetal 

 rat or mouse will answer the purpose equally well. 



With a sharp knife, cut transverse sections, about Jth inch 

 thick, from the following regions : a, snout ; b t cranial 

 region; c, neck ; d, thorax; and e, abdomen. Stain and 

 embed, and then cut and mount one or two sections of each, 

 examining them with a low power and making sketches. 



Then put on the high power, and make out as much as 

 possible of the histology of the various organs. 



