THE MAMMALIAN NERVOUS SYSTEM 45 



ing of the functional connections of the various parts of the 

 nervous system, and this end should be constantly kept in 

 mind. Daily consultation of reference books in connection 

 with each structure 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 arbi- 

 trarily into subdivisions which are more clearly defined in the 

 embryonic 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 develop- 

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

 with illustrations of the His models: Bailey and Miller ('16), 

 pp. 532-557; Gray ('18), pp. 733-749; Herrick ('18), Chap. 

 VII; His ('04); Keibel and Mall ('10), Vol. II, pp. 29-106; 

 Piersol ('16), pp. 1059-1063. Almost every text-book of 

 human anatomy and embryology includes some account of 

 these questions and "pictures of the models. The official list 

 of B N A terms is reprinted in Eycleshymer's Anatomical 

 Names ('17) and also a translation of the annotations by Pro- 

 fessor 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. 



