62 EXEKCISE IX 



space, and posterior border of first rib. Refer to the cat's skeleton provided 

 in the class-room and note the shape of the first and second ribs. Scrape 

 bare the dorsal edge and anterior and posterior faces of the second rib 

 from its articulation out laterally to the already detached serratus magnus, 

 thus exposing about 4 cm. of the rib. Carefully dissect away the muscular 

 sheet of the first intercostal space for the area demarcated by the bared 

 portion of the second and first ribs. 



With the oblique-edged cutting-pliers cut carefully through* the second rib 

 at its farthest laterally-cleared part; seize with strong forceps the rib so 

 cut closely medial to the cut point ; lift it and carefully free its deep surface. 

 The subclavian vein must not be wounded. Remove the piece of the rib 

 thus freed. 



Ganglion stellatum (PL lY, fig. 4), the most anterior of the thoracic 

 ganglia of the sympathetic, can be seen lying about 5 mm. lateral to the 

 median edge of the window in the chest cavity. Fat in somewhat tough 

 connective tissue lies near, especially lateral. A small artery passes obliquely 

 lateral and headward of the ganglion. Posterior to the ganglion, in the cut edge 

 of the muscles dissected from the posterior edge of the second rib, is the second 

 intercostal nerve ; at this nerve's extreme proximal course a fine branch passes 

 from it to the ganglion ; this is the white ramus communicans of the second 

 thoracic nerve. Headward of the ganglion, partly covered by first rib, is a large 

 nerve running almost parallel with the edge of the rib ; this is the first thoracic 

 nerve going to the brachial plexus. A small branch from the median edge of 

 the anterior end of the ganglion is seen passing towards the first thoracic nerve ; 

 this is a grey (post-ganglionic) ramus. 



The ganglion is seen to have two other branches : 



(a) from its posterior end a largish branch ; this is the main cord of the 

 sympathetic and passes to connect with the vertebral ganglion of 

 the sympathetic next behind the stellatum itself. 



[h) a branch from the top of the ganglion passing directly headward ; this 

 enters the neck as the cervical sympathetic. 



Ligate with fine silk [a) and (&), also the white ramus from' second thoracic 

 nerve. Cut these branches on the side of the ligatures remote from the 

 ganglion. 



Lifting the ganglion (PL IV, fig. 5) somewhat by drawing on one or other 

 of these ligatures, free it gradually by snipping carefully the thin tough 

 connective tissue which binds it down. As it is freed and lifted, branches 

 (usually double) are clearly seen passing ventrally from the ganglion and 

 sloping towards the sternum (to reach vena cava superior). Also two branches 



