202 DR. PETTIGREW ON THE MECHANISM OF FLIGHT. 



\\ nigs and by muscular efforts, as happens in the Lark. The bird can in this manner 

 likewise retain its position in the air, as may be observed in the Hawk when hovering 

 above its prey (Plate XV. fig. 60). If birds wish to descend, they may reverse the di- 

 i ion of the inclined plane and plunge head foremost with extended wings (Plate XIV. 

 figs. 34 and 86); or they may flex the wing (Plate XIV. fig. 33), and so accelerate 

 tli eir pace; or they may raise their wings and drop parachute-fashion (Plate XIV. 

 tiu->. : > and 40); or they may even fly in a downward direction — a few sudden strokes, 

 a more or hm abrupt curve, and a certain degree of horizontal movement being in either 

 ca-i* necessary to break the fall previous to alighting. Birds which fish on the wing, as 

 the Osprey and Gannet, precipitate themselves from incredible heights and drop into 

 the water with the velocity and power of a cannon-ball — the momentum which they 

 acquire during their descent materially aiding them in their subaqueous flight. They 

 emerge from the water and are again upon the wing before the eddies occasioned by then 

 pivcipitons descent have well subsided, in some cases rising apparently without effort, 

 and in others running along and beating the surface of the water for a brief term with 



their pinions and fi 



The Flight of JJirda referable to Muscular Exertion and Weight. — The various move- 

 ments involved in ascending, descending, wheeling, gliding, and progressing hori- 

 zontally are all the result of muscular power and weight, properly directed and act- 

 ing upon appropriate surfaces— that apparent buoyancy in birds which we so highly 

 esteem arising not from superior lightness, but from their possessing that degree of 

 solidity which enables them to subjugate the air,— weight and independent motion, i. e. 

 motion associated with, animal life, or what is equivalent thereto, being the two things 

 indispensable in sucessful aerial progression. The weight in insects and birds is in great 

 measure owing to their greatly developed muscular system, this being in that delicate 

 state of tonicity which enables them to act through its instrumentality with marvel- 

 lous dexterity and power, and to expend or reserve their energies, which they can do 

 with the utmost exactitude, in their apparently interminable flights. As space will not 

 admit of my going into the muscular arrangements of birds, I may state, as has been 

 already partly done (pp. 200, 201, and 202), that this branch of the subject would 

 lose much of its intricacy, if, instead of regarding the muscular system of the win? 



of flexor, extensor, abductor, adductor, pronator, and supinator urns 



D 



cles, we were to regard it as consisting of a series of muscular cycles or rings with the 

 bones and intervening joints as their diameters,-contraction on the one aspect of the 

 circle, whether above, below, or at the sides of the bone, being accompanied by relaxa- 

 tion on the other, the bones and joints, which may be regarded as oscillating within the 



muscular cycles, making the muscular efforts apparent by the flexion, extension, and 

 upward and downward movements of the pinion *. 



* This view, as has been explained, is rendered probable bv the fact tW ;« rt. i u- *,-««« nf 



™„ „i*. „„-*ii * . i , i , , , " lM Iact tnat in the more elementary combinations oi 



muscles, as m the heart, stomach, b adder, and uterus and in t>> „„, i i , • n„ 



arrant « i ♦• \ , Vermes and leeches > the muscular fibres are spirally 



arranged and are continuous upon themselves— and because the «H f m,,«nr^ . • , ,-, , * ■ .„,« 



. ( ., j M . * "".au&einebcitrousor bony parts in the higher orders of animals are 



added as supports, and are by no means essential to motion Tt i* ™™ • ., , , • ♦!„> 



neniliar «*U« „f i motion, it is, moreover, next to impossible to determine the 

 peculiar action of anv one muscle nn nnv nno norf „« *i . .*.%... r 



