Dec. 30, 1886] 



NA TURE 



209 



This scheme I propose to modify in certain particulars. For 

 the sake of clearness I give diagrams (Fig. i) showing three im- 

 portant stages in the development of the brain, as well as draw- 

 ings of the brain o^ Scymniis Ikhia (Fig. 2). The latter shows 

 with such diagrammatic clearness the typical structure of the 

 Vertebrate encephalon that I now always use it as a starting- 

 point for the study of that organ in my lectures. 



(a) I propose to follow Wilder in his use of the words neuron 

 and neurocoele, encephalon and encephalocoele, myelon and 

 myelocrele ( Fij. I, a). The words syringocoele and rhombocoele 



appear to me unnecessary : I prefer to say that in some Verte- 

 brates (e.g. birds) the lumbar region of the myelocoele is dilated 

 into a sinus rhomboidalis. 



(Ii) The three primary cerebral vesicles may be called respect- 

 ively the protcnccphalon, deuteyencephalon, and trit nreplialon ; 

 their cavities the protocccle, deiiteroccele, and (primary) Irilocale 

 (Fig. I, A). 



(f) In what may be called the sub-primary stage of segmenta- 

 tion, the anterior, or first, and theposterior, or third, cerebral vesicles 

 have each divided into two parts, the brain thus consisting of 



Fig. z. — Five views of the brain of Scyimws Uchia (r^at. size). A. dorsal view of the brain, entire, save for the rei 

 {I'el.int) and tela vasculosa (U/.vasc) on the right side. E, the same, with the cavities opened from above, c, the 

 entire brain from the left side. E, longitudinal vertical section. The letters have the same significance as in Fig. i, 

 vasculosus) ; vel.int, velum interpositum ; tel.Tosc, tela vasculosa ; and ii-x, cerebral nerves. 



five encephalomeres, which I propose to call respectively the 

 pivsthiencephalon (= prosencephalon of Quain, Vorderhirn) and 

 diencephalon (= thalamencephalon), derived from the prot- 

 cnccphalon ; mesencephalon (identical with the deuterencephalon), 

 epetictphalon, and meteiiccphalon, formed by the constriction of 

 the primitive tritencephalon. The cavities of these five brain- 

 segments will be ^s prosthio-, dia-, ?neso-, epi-, and mcta-ca;!es 

 (Fig. I, B). 



(</) In the next stage of differentiation of the fore-brain, the 

 prosthiencephalon gives rise dorsally to the two cerebral hemi- 

 spheres : I propose to follow Owen and Hu.xley in calling them 

 the prosencephala (Fig. 1, c and d; Fig. 2, A — E, prosen); 



Tioval of the velum interpositum 

 entire brain from below. D, the 

 e,\cept heevt, haematosac (saccus 



their cavities, or lateral ventricles, being named prosoccsles 

 (fii-s.ca-). The median portion of the prosthiencephalon, 

 after separation of the prosencephala, may be called the l/asi- 

 cerelmwi (b.cbr.) ; its cavity, the aula, is Y-shaped, communi- 

 cating by its unpaired posterior limb with the diacoele, by its 

 paired anterior limbs with the prosocceles through the Joramina 

 of Monro (for. M), o\ porUe. The two prosencephala rnay be 

 spoken of collectively by the old name, cerebrum, which, as 

 Pye-Smith remarks,^ "ought to be strictly limited to the hemi- 

 spheres with the corpus callosum, corpora striata, and fornix. 



* " .Suggestions on some Points of Anatomical Nomenclatur " Joum, 

 ofAnat. cindPhys., xii. (1878), p. 154. 



