CHAPTER X. 



ENCEPHALON — THE BRAIN. 



GENERAL CONSIDEEATIONS — NAMES OP THE PEINCIPAL PARTS OP THE AMPHIBIAN BRAIN 

 — ^DIAGRAMS OP AN IDEAL SIMPLE BRAIN— EXAMINATION OP THE BRAINS OP THE 

 PROG AND MBNOERANCHUB — REMOVAL OP THE CAT'S BRAIN — MACROSCOPIC VOCABO- 

 LART— DESCRIPTION OP PIGIIRES AND PLATES— DISSECTION OP THE BRAIN — 

 STNONTMS AND REPBRENCBS — PISSDEES AND GYRI. 



§ 1049. G-eneral Considerations. — Definition. — Excluding Am- 

 phioxus, whose brain is peculiar and apparently incomplete, the 

 vertebrate encephalon may be defined as the enlarged, differenti- 

 ated and incompletely segmented cephalic portion of the myelen- 

 cephalon (cerebro-spinal axis), contained within the cranium,. 



The junction of the brain proper with the myelon proper (§ 1006, Fig. 104) is formed 

 by the part commonly called meduUii (oblongata), but metencephalon by Quain (A, II, 755), 

 and in the prespnt work. By its obvious characters and real structure the medulla is 

 only a modified continuation of the myelon (Strieker, A, 758-764, Spitzka, 1, 46), and 

 Wyman describes it (34, 7) as a division thereof; most writers, however, regard it as a 

 part of the brain, and this is prncticiUy the more convenient way. 



§ lOoO. Importance and Difficulty of the Study of the Brain. — An acquaintance with 

 the obvious features, the intimate structure and the functions of the brain is desired by 

 not only the physician and the practical veterinarian, but also by the systematic zoologist, 

 the comparative anatomist, the physiologist and the psychologist. 



The nature and extent of the obstacles to the acquisition of this knowledge are most 

 fully appreciated by those who have advanced the farthest in its pursuit ; some idea of 

 them may be gained from any recent compendium by an original investigator in either 

 of the branches of inquiry above indicated (Quain, A, II ; Strieker, A ; Ferrier, A). 



Deferring for the present any considerations of the histology and functions of the 

 mammalian brain, its mere topography is far from easy to understand. 



§ 1051. Methods of Studying the Brain. — The brain is com- 

 monly figured and described as a fibrous and cellular mass pene- 

 trated here and there by inconsiderable cavities. Little attention is 

 paid to the membranes which line these cavities and invest the 

 entire organ. Stress is laid upon its complex structure and remark- 



