ANATOMICAL DESCRIPTION 295 



plexuses, fibers from which accompany the blood vessels 

 throughout the body, penetrating to all parts of the various 

 organs. In the abdomen is found also a great plexus of 

 nerve fiber called the solar plexus, because smaller plexuses 

 radiate from it like rays of light from the sun (Fig. 137). 

 From the solar plexus nerve filaments are distributed to all 

 the abdominal organs. 



DEMONSTRATION 



125. Dissection of the Brain. The specimens used in Ex. 6 (p. 33) 

 should now be studied more in detail. The brain should be divided 

 into two symmetrical halves, and the longitudinal median section, thus 

 exposed, should be compared with Fig. 129. In this way all the parts 

 of special importance can be identified. Care should be taken that 

 the pupil makes this careful detailed comparison and identification. 

 Slice away the dorsal (upper) surface of the cerebrum till a cavity, 

 the lateral ventricle, is reached. By carefully removing the roof of 

 this cavity the latter is seen to extend forward and downward as the 

 anterior cornu, and downward and backward as the descending cornu. 

 The corpus striatum is an oval mass projecting into the cavity of the 

 anterior cornu. The hippocampus is an oval projection forming the floor 

 of the posterior part of the lateral ventricle, including the descending 

 cornu. Between the corpus striatum and the hippocampus extends 

 a fibrous band, the descending pillars of the fornix. This band can 

 be traced to the middle line and seen to be a part of the fornix 

 cut in the median section. Cut away the hippocampus and the band 

 of the fornix; the optic thalamus is exposed (see Fig. 130). Posterior 

 to the thalamus are the two corpora quadrigemina of that half of the 

 brain. Between the descending pillars of the fornix and the optic 

 thalamus is a narrow opening, the foramen of Munro, which commu- 

 nicates with the third ventricle and through the latter with its fellow 

 of the opposite half of the brain. By this means the two lateral ven- 

 tricles communicate with each other and with the other cavities of 

 the brain. 



The cerebellum will be found on close examination to be attached 

 to the rest of the brain by three pairs of fibrous bands. One pair, 



