B I R 



B I R 



it defccnds, it receives a broad flip of nnifcic from the back 

 of the femur. It is iiiferted on the back of the tibia, and 

 tlic tendon covering the cxtenfors of tlie heel. 



There is a large ranfcle on the infide of the thitrh, which 

 fupplics the place of the triceps. It performs adduction, but 

 it is alfo employed in carrying the limb backwards. 



A mufcle, which Cuvier appears to reckon as the feconcl 

 addud.or, arife? from the back of the ifchium, and is inferted 

 into the middle of the femur in company with the crura- 

 coccygeus mufcle. It retracts the limb. 



The mufcles for extending the heel, and confequently the 

 lower part of the leg of birds, differ in many refpefts from 

 the gaftrocnemn ot mammalia. The tcndo achillis is pro- 

 duced by three portions of mufcle ; and, after pafling over a 

 moveable cartilaginous pulley which is placed on the heel, 

 it fpreads on the fides of the metatarfal bone. The firil 

 portion anfes from the inner and fore part of the joint of 

 the knee, and is connefted for fome way with another muf- 

 cle, which lies on the outfide of the joint. The fecond 

 portion is fmall, and from the back of the internal condyle 

 of the femur. The tliird is a very flrong mufcle arifnig by 

 tendon from the outfide of the thigh bone, jull above the 

 condyle. Thele three heads appear to be the external gnf- 

 trocnemius, 



Thc/o!eus is reprefented by a mufcle which arifes from 

 the outer part of the knee joint, from the upper part of the 

 tibia, and fi'om the fore part of the fibula. ■ It i« inferted 

 into the pulley on the heel, and fends a tendon to join that 

 of the fle.\or of the lirft phalanx of the toes ; and therefore 

 it bends the toes while it atis on the heel. 



There is alto a mufcle which appears to fupply the place 

 of the pliinlaris. It comes from the back of the head of 

 the tibia, and affixes its delicate tendon to the infide of 

 the moveable pulley of the heel. 



The tiblalu aiiticus arifes by two head.", and is inferted into 

 the fore part of the upper end of the metatarfal bone. It 

 bends the joint of the heel. 



The tibialis pojiicus is not found in birds. 



There is a fnort peroneal vwiitAv. which is inferted into the 

 outfide of the metatarfal bone. It merely bends the 

 joint. 



The other mufcles fituated along the legs, are for the 

 flexion and extenfion of the toes. The extenfor longus digi- 

 icrum exhibits no peculiarity, except that its ttndon goes 

 through a hole in the end of the tibia. There is no hrg ex- 

 ievjur for the back toe. 



The_/7i'.v rs of the toes are very complicated : they may be 

 diviilcd into \^i\i Jlexor fuHiinis 2,\\& Jlexor profundus. The 

 firlt is compofed of fcvcval portions ; two of thcie are pero- 

 neal mufcles, and fend their tendons to the firfl: joint of 

 the intern:;! toe and the fecond phal.inx of the middle toe ; 

 the two other portions of \.\ie Jie>:or fublirnis arife, one from 

 the outfide of the fibula, and the other from the back of 

 the joint and internal co:"d\le of the femur. The one on the 

 fibular fide is joined by the tendon of the accejforius femo- 

 rcTis f.ixorum : a mufcle, which arifts from the fpine of 

 the pubis', runs along the thigh, and lends its tendon 

 through a (heath that runs over the hgamcnt of the patella, 

 to arrive on the fibular fide ot the leg. The two porcions of 

 the flexor, after this, unite, fcparate, and unite again, and 

 at laft produce three tendons, of which two go to the firtt 

 phalanges of the intcri;al and middle toes, and the tliird to 

 ail the joints of the outer toe except the laif. Thole ten- 

 dons which pafs beyond the firft joint, are perforating as 

 w el as perforated. 



'YW fit xor profundus arifes as two diHinft mufcles; the 

 one from the back of the femur, and the other from the 



back of the bones of the leg. The two tendons unite on 

 the back of the metatarfal bone, and fend off tendons to the 

 lall phalanges of the toes, which perforate thofc of the flexor 

 fubhmis. 



All the flexor tendons are inclofed in a tendinous (heath, 

 as they pafs along the back of the metatarfus ; and fome 

 of them go through the moveable cai-tilaginous pulley of 

 the heel, and others run in (heaths formed in the cartilage 

 which covers the top of the metatarfal bone. 



The circumftance of tiie flexion of the toes accompany- 

 ing that of the other joints of the lower extremity of birds, 

 was long ago obferved by Borelli, and attributed by him to 

 the connexion the flexors of the toei have with the upper 

 parts of the limb, by which they are mechanically llretched 

 when the knee is bent. This explanation has been contro- 

 verted by Vic d'Ay.ir and others, who have referred the ef- 

 feft to the irritability of the mufcles. Tne opinion of Bo- 

 relli appears, notwithftanding, to be well founded ; for not 

 only the tendon of the acceffory flexor pafling round the 

 knee, but the courfe of the flexor tendons over the heel 

 and along the metatarfus, mull neceffarily caufe the con- 

 traftion of the toes, when either of thefe joints are bent ; 

 and if the phenomenon was not produced on mechanic prin- 

 ciples, it would be impoflible for birds to exhibit it dur- 

 ing fleep, wliich they do, or to prove the effect on the li.T.b 

 of a dead bird, than which nothing is more eafy. The 

 utility of this contrivance is great in all birds, but particu- 

 larly fo to tiie rapacious tribe, v.hich by this means grafp 

 their prey in the very aft of pouncing on it ; and it ii ilill 

 more neceffar)- to thofe birds which perch or rooft during 

 their deep, as they could not otherwife preferve their po- 

 fition when all their voluntary powers are fufpended. 



There are fix long fmall mufcles lying on the metatarfal 

 bone ; they are largeft and bell marked in thofe birds which 

 walk moft. Two of thefe are on the poflerior furface ; one 

 goes to the bafe of the external toe, which it abducls ; the 

 other i.^ inferted into the root of the back toe, which it bendt^ 

 On the anterior part of the metatarfus there are four mufcles : 

 the firfl extends the back toe ; the fecond goes to the bafe cf 

 the firfl toe, and abducts it ; the third is fpread on the root 

 of the middle toe, which it extends ; the fourth lies along 

 the outfide of the metatarfus, perforates the end ot tlie bone, 

 and \z implanted into the infide of the external toe, a:;d ad- 

 duds it. 



Brain. 



This organ exhibits fevcral deviation.^ from the flrufture oF 

 the brain of mammaha, which afterwards appear in a more 

 marked manner in the inferior claffes of animals. Accordingly, 

 in the fcale of exHtence, or with refpetl to fenfitive or mental 

 faculties, the rank of birds is clearly fixed below that of 

 mammalia, and above that of other animals. The rules which 

 have been ellablifhed to determine the degree of iDtelligcnce 

 pofTeffed by fpecies or individuals, according to llie piopor- 

 tion the brain bears to the wiiole body, or other parts of 

 the nervous fyllem, do not appear fo applicable in birds as 

 in mammalia. It is, however, very difficult to appreciate the 

 capacity of birds, as they ai-e fo much the flaves of inllinCt, 

 that it is often impolTible to difcover v\'hethcr their adions 

 arife from the unpiilfe of this principle, or depend upou the 

 recoUeftiun and affoeiation of external fenfations. The 

 largeft birds generally have the fmallcll proportion of brain 

 t.) the whole body ; and fome of t!ie fmall birds have the 

 proportion of brain fo great, that they would, agreeable to 

 the rules laid down, excell ia mental endowments man him- 

 felf : for i:;(la'.;ce, the brain of the canary bird is equal to 

 tlie one fourth of the whole body ; and in the liuman fub- 

 jed it is only the one-twcnty-tifth part. The diamtter o£ 



the 



