84 ANATOaiY OF VERTEBRATES. 



CHAPTER XV. 



MUSCULAR SYSTEM OF AVES. 



§ 131. General Characters. — The muscular system of Birds is 

 remarkable for the distinctness and density of the fasciculi or 

 visible fibres, the deep red colour of those chiefly employed in 

 vigorous action, and their marked separation from the tendons, 

 which are of a pearly shining colour, and have a peculiar 

 tendency to ossification. This high degree of developement re- 

 sults from the rapid circulation of very warm and rich blood, 

 highly oxygenated through the extent of the respiratory system. 

 The energy of the muscular contraction in this class is in the 

 ratio of the activity of the vital functions, but the irritability of 

 the fibre rapidly goes after death. The elementary fibres are 

 much smaller and less sharply angular than in Reptiles ; the 

 blood-vessels being more abundant and occupying more space in 

 their intervals. 



These characteristic properties are manifested in the greatest 

 degree in the muscles of the Volitores, and of those Cantores that 

 take their food on the wing, as the HirundinidcB ; in those of the 

 Diurnal Raptores and the long-winged Palmipedes, as the Alba- 

 tross, Tropic Bird, &c. In the more heavy and slow-moving 

 Herbivorous families, the muscles resemble those of the Reptilia 

 in their softness and pale colour. In birds of flight the me- 

 chanical disposition of the muscular system is admirably adapted 

 to the aerial locomotion of this class ; the principal masses being 

 collected below the centre of gravity, beneath the sternum, beneath 

 the pelvis, and upon the thighs, they act like the ballast of a 

 vessel and assist in maintaining the steadiness of the body during 

 flight, Avhile at the same time the extremities require only long 

 and thin tendons for the communication of the muscular influence 

 to them, and are thereby rendered light and slender. 



§ 132. Muscles of the vertebrcB.—Tha muscles of the cervical re- 

 gion are the most developed, as might be expected from the size 

 and mobility of this part of the spine ; the muscles which are situ- 

 ated on the dorsal and lumbar regions are, on the other hand, very 

 indistinct, feeble, and but slightly carneous ; they are not, how- 



