B I R 



the brain, in relation to the medulla oblongata, has beenaf- 

 ccrtaincd only in a few fpccies of birds, in which it has been 

 obfervcd as follows : 



Falcon - -• . 



Owl ... 



Duck 



Turkey . - - 



Sparrow 



The brain of birds is inrefted 

 which are dcfcribcd in mammalia. 



The /orm of the cerebral mafs is very different from that 

 of the human brain, wliich chiefly arifes from the optic tha- 

 lamic being vifible externally. The hemifpheres arc therefore 

 proportionately diniinilhcd. They afruiiie the fhape of a 

 heart with the point turned forwards. On the lower part of 

 the fide of the licmifpiiere, there is a dcpreffion which corre- 

 fponds to the f'Ja of Sylvius, and is the only appearance of 

 a divilion into /oifj. Underneath the hemifpheres the ihafa- 

 mi nfivoriim opiicorum arc found, as two diltinft tubercle", each 

 equalling in magnitude a lobe or divlfion of the brain. Tliey 

 unite before the infundibulum, and fend off the optic nerves; 

 there are, therefore, fix parts, or principal eminences, of 

 the brain of birds, vifible externally ; the two hemifpheres, 

 the two thalami, the cerebellum, and the medulla oblongata. 

 There are no convolutions, or winding impreffions, on the 

 furface of any of thefe parts, except the cerebellum, which 

 is tranfverfely furrowed, but not divided into two lobes. 

 The medulla oblongata is round, and fmooth on the under fur- 

 face, being u\ifurni(lied with the eminences called pons Var- 

 olii, corpora pyramiilalia, and corpora olivaria. 



On fLparating the hemifpheres a little, it is perceived that 

 they are united at their lower part, or over the third ventri- 

 cle. The junction is cfTefted by white medullary fubllance, 

 which afterwards fpreads in a radiated manner, on the furfaces 

 of the hemifplieres that are oppofed or applied to each other, 

 almoll as high as the top of the cerebrum. In reality, this 

 medullary union of the hemifpheres correfponds to i\\t fornix, 

 and can, like it, be traced to the anterior commillure in the 

 third ventricle ; but inftead of being connefted to the fep- 

 tum lucidum and lorpus callofum, as thefe parts do not exill 

 in birds, it fpreads on the inner furfaces of the hemifpheres, 

 and thus contributes to form the internal parietes of the 

 lateral v«ntricles. 



Behind the radiated partition of the hemifplicres, and 

 without the third ventricle, the pojlerior commijfure prefents 

 itfelf, and confills ufually of more than one vvliite line con- 

 Beftcd together by a white fibre, like a nerve pafiing obliquely 

 acrofs. The vault of the canalis nuilius is alfo vilible, and 

 is compofed in part of a white medullary band ; and behind 

 this, another white cord runs acrofs, which is the fourth 

 pair of nerves at their origin. 



The lateral ventricles are not prolonged poflenorly, nor 

 poffefs what is called the rcpclcd horn ; the great and lejfer 

 hippocampus have therefore no exillence. 



The corpus Jlriutum fills the ventricle almoft entirely, pro- 

 jefting from the external fide of it in the fliape of a kidney. 

 It docs not exhibit on a fcclion regular or ilrong marked 

 llrix. 



There are no iuiercula quaJrigemina. 



The pineal gland rcfls upon a flat furface ; it is very 

 fmall, and invcloped in pia mater, and covered by a large 

 vein. The plexus choroides alfo at this place divides 

 into two tutts, or bunches, which pafs into the lateral 

 ventricles by two foramina in the back of the internal 

 parietes. 



6 



B I R 



Tlie third ventricle pofTefTes its ufual fltuatlon between tl« 

 thalami and its flit-like fhape, and communicates with theca- 

 nalis medius under the poilenor commifTure, and with the in- 

 fundibulum behind the anterior commiffure. 



The infundihulum and pituitary gland are both large in pro- 

 portion to the other parts. 



The thalami nervorum oplicorum contain each a ventricle, 

 which opens into the canalis medius; therefore, there may- 

 be fix ventricles rccknned in the brain of birds. 



The fourth ventricle exhibits no peculiarity. 



There are no eminences correfponding to the corpora 

 candicanlhi ; Cuvier has defcribcd four round eminences be- 

 tween the thalami and corpora flriata, which are particularly 

 plain in the oflrich. Thefe are analogoui to the tubercles of 

 the brain of fiflief. 



The olfactory nerves arife, in birdo, from the very points 

 of the Iiemifpheres, and often have a degree of enlargement 

 at their origiii, which refcmbles the olfaftory tubercles of 

 fifhes. There are eight other pair of cerebral nerves, which 

 have nothing very peculiar in their origin. 



See Plate X. of the Anatnmy of Birds. Fig. i. prefents a 

 lateral view of the brain of the goofe abftraded from the liead; 

 a the hemifphere, 6 the depreflion analogous to the fiifura 

 Sylvii, c the optic thalamus, d the cerebellum, e the me- 

 dul'a oblongata, / the beginning of the medulla fpinalis, g 

 tiie infundibulum, h the pituitary gland. The diiTereut 

 nerves are indicated by nunnbers, as they arife, from i to 9. 

 N° I. the olfaftory nerve, N" 2. the optic, N" 3. the ocu- 

 lo-mufcular nerve, N° 4. the patheticus, N'-' 5. the trifacial 

 nerves, N°6. the nervus abducens, N'7. the feventh pair, 

 or auditory, N'^ 8. the eigl'.th pair, N'^ 9. the hypoglofTal 

 nerve. 



Fig, 2. of the fame plate, fhcws the internal parts of the 

 brain, as they are expofcd without diffedlion, fimply by 

 pufiiing the hemifpheres to each fide, and drawing the ce- 

 rebellum a little back : aa the two hemifpheres, i the cere- 

 bellum, c the medulla oblongata, ee the radiated white lines 

 feen arifing from the jundlion of the hemifpheres, and form- 

 ing part of the parietes of the lateral ventricles, f the 

 tranfvcrfe medullary cords correfponding to the pollerior 

 commiffure, g the wliite baud of the root of the canalis me- 

 dius, h the fourth pair of nerves crofllng behind it, i the 

 pineal gland obfcured by the vena galeni and the plexus 

 choroides, h the latter paffing into the ventricle. 



The third figure of the tenth plate of the Anatomy of 

 Birds, gives a view of the interior of the ventricles of the 

 thalami nervorum opticorum, and the third ventricle : a a 

 the hemifpheres laid down very much to each fide, by 

 which the white paitition is ruptured, and the third ven- 

 tricle brought into view, they are alfo palled forwards to 

 expofe the thalami ; b the cerebellum ; c the medulla oblon- 

 gata ; dd the two optic thalami, that on the right fide i» 

 cut open to ihew the ventricle and its communication with 

 the canalis medius ; e the traCl of the third ventricle and 

 canalis medius, along which a brilUe is pafTed into the fourth 

 ventricle ; y the anterior commilTure, which feeins to produce 

 the medullary radii that unite the hemifpheres. 

 Nerves. 



The olfa8ory nerve has been already mentioned to pafs 

 along a canal, or groove, in the upper and inner part of the 

 orbit, to reach the nafal cavity; in which its dillribution 

 will be pointed out in defcribing the organ of fmell. 



The optic nerves purfue their ordinary courfe, as in other 

 animals. 



The dillribution of the third, fourth, dnd Jlxlh pair of 

 nerves, is almoft the fame as in mammalia. 



The branches of the fifth pair bear great referablance to 



the 



