THE MAMMALIAN NERVOUS SYSTEM 43 



consultation of reference books in connection with each struc- 

 ture studied in the laboratory is indispensable. The fiber tracts 

 should be related to each other .in functional systems of reflex 

 arcs as rapidly as possible. Compare the lists given in the 

 sections devoted to the recapitulation of conduction paths 

 (Sections 101 and 153). 



38. Subdivisions of the brain. — For convenience of study the 

 central nervous system has been separated somewhat arbitrarily 

 into subdivisions which are more clearly defined in the embry- 

 onic brain. These subdivisions should be identified on a series 

 of wax models of developmental stages of the human brain, such 

 as the His models manufactured by Ziegler, and also on the 

 adult brains of man and other mammals. 



The following references include accounts of the development 

 of the brain and the principles of its subdivision, together with 

 illustrations of the His models: Bailey and Miller ('16), pp. 532- 

 557; Herrick ('15), Chap. VII; His ('04); Keibel and Mall ('10), 

 Vol. II, pp. 29-106; Sheldon ('18), Chaps. I to III. Almost 

 every text-book of human anatomy and embryology includes 

 some account of these questions and pictures of the models. 

 The official list of BNA terms is reprinted in Eycleshymer's 

 Anatomical Names ('17) and also a translation of the annota- 

 tions by Professor His on the neurological terms (pp. 153-174). 



39. Brain of fetal pig. — Take two pig embryos, about 3 cm. 

 and about 5 cm. in length respectively, which have been pre- 

 served in 10 per cent, formalin. Dissect out the brains from 

 the side, or else cut the embryos in the median sagittal plane. 

 The larger embryo can be more conveniently dissected and the 

 smaller one sectioned. They may be stained for five minutes 

 in a dilute solution of methylene-blue (about 1 part in 10,000 

 parts water) if desired. Determine the five brain vesicles with 

 the aid of a dissecting microscope or a hand lens, draw them, and 

 compare them with the His models and the adult brain. This 

 is the procedure followed in the Anatomical Laboratory of Johns 

 Hopkins University, for which we are indebted to Dr. E. V. 

 Cowdry. 



40. Here review the dissection of the fish brain and determine 

 the precise limits of its chief subdivisions in comparison with 

 those of the embryonic human brain. Note particularly the 



