482 ANATOMICAL TECHNOLOGY. 



1263. Mesocoelia (az.\ msc Fig. 110-113, 117; PI. II, Fig. 4; 1055. Gray, A, 

 030 ; Quain, A, II, 552. 



Syn. Aquseductus Sylvii, iter a tertio ad quartum ventriculum, ventriculus opticus, 

 ventriculus mescncephali. 



The mesencephalic cavity, enclosed by the crura cerebri, the optici and postoptici, and 

 opening cephalad into the diaccelia and caudad into the epiccelia. 



1264. Metacoelia (az.), mtc.Fig. 113, 117 ; PI. II, Fig. 4 ; 1065. Gray, A, 635 ; 

 Quain, A, II, 512. 



Syn. Ventriculus quartus, caudal portion. As has been admitted ( 1225), it is diffi- 

 cult, perhaps impossible, to define accurately the limits of the metacoelia and epiccelia. 



1265. Metaplexus, mtpx. Fig. 116 ; PI. II, Fig. 3. Luschka, A, PI. Ill ; Gray, A, 

 636 ; Quain, A, II, 513. 



Syn. Plexus choroideus ventriculi quarti, plexus choroideus inferior. 



We have not yet satisfied ourselves respecting the nature and connections of this 

 plexus, and have provisionally designated the prominent plexus between the dorsal border 

 of the medulla and the cerebellum as the metaplexus lateralis. 



1266. Metencephalon (as), mten.Fig. 110-113, 116; PI. I, Fig. 1, 2; PI. II, Fig. 

 3, 4; PI. Ill, Fig. 12. Gray, A, 111 ; Quain, A, II, 753. 



Syn. Medulla, as far as the pons. See 1061, 1225. 



1267. Metatela (az.\ mttl.F\g. Ill, 112, 116; PI. II, Fig. 4; PI. Ill, Fig. 12. 

 Luschka, A, PI. III. 



Syn. Tela choroidea inferior. 



Notwithstanding this atrophied roof of the metacoelia is so obvious with Amphibia as 

 to have been once mistaken for the cerebellum, it is usually ignored in the dissection of 

 the mammalian brain, probably because of its tenuity and its liability to be torn off with 

 the cerebellum. 



As has been stated in several places, there is much to be learned respecting the struc- 

 ture of the metatela, the arrangement of the metaplexus and the " Foramen of Magendie." 

 The probability of the existence of the latter is increased by the experiments of Wett- 

 brook ( 1), which should be repeated upon the cat ; detailed descriptions and enlarged 

 figures are required ( 1082). 



1268. Myelon (az.), my. Fig. 88, 104, 109-113, 116; PI. I, Fig. 1, 2 ; PI. II, Fig. 

 3, 4. Gray, A, 604 ; Quain, A, II, 489. 



Syn. Medulla spinalis, spinal cord, spinal marrow, chorda spinalis. 



It is described in 1006 and in connection with the figures above named. 



1269. Nervus abducens, N. nb. This and the other cranial nerves (i-xii) are 

 treated of in the next chapter. The ectal origins are shown in Fig. 116 and in PI. II, 

 Fig. 3. 



1270. Obex, ob. We have not yet identified this in the cat. It is mentioned by 

 Spitzka (3, 18), and also, we think, by Meynert (Strieker, A). 



1271. Oliva, olv. According to the Am. Jour, of Neurology, etc. (I, 102), the eleva- 

 tion called Area elliptica (Fig. 116 ; PI. II, Fig. 3, Ar. el.) represents the olica or Corpus 

 olixarium, notwithstanding the funiculi of the N. hypoglossus emerge laterad of it. 



1272. Opticus (Lobus), op. Fig. 110-112, 114, 116, 117; PI. II, Fig. 4; PI. Ill, 

 Fig. 7, 8, 9, 12 ; PI. IV, Fig. 18, 19 ; 1142. Gray, A, 631 ; Quain, A, II, 551. 



Syn. Corpus bigeminum anterius, natis cerebri, one of the corpora quaclrigemina, 

 cephalic lobe of the mesencephalon. 



As seen in PI. Ill, Fig. 7, 8, 9, the opticus is more regularly convex and less elevated 

 than the postopticus. 



