270 



AVKS. 



also their neck. Their dense plumage is oiled 

 and lubricated by the secretion of the coccy- 

 geal glands, which are remarkably developed 

 for that purpose. In general the males have 

 many females, and in harmony with this spe- 

 ciality the young are hatched in a condition 

 which renders the cooperation of both parents 

 for their support unnecessary, being able to 

 take to the water and swim about in searcli 

 of food the instant that they are liberated from 

 the egg-coverings. The families of Swimmers 

 are the Anatidts, Swan, Goose, Duck; Co- 

 lymbidee, Divers; Alcad/p, Auks ; Pelecanida, 

 Pelican, Cormorant, Gannet ; Laridee, Gulls. 



1. Osteology. The skeleton of Birds is re- 

 markable for the rapidity of its development 

 and the light and elegant mechanism displayed 

 in the adaptation of its several parts. The 

 osseous substance is compact, and exhibits 

 more of the laminated and less of the fibrous 

 texture than in the other vertebrate classes. 

 This is more especially the case in those parts 

 of the skeleton which are permeated by the air. 

 The bones which present this singular modifi- 

 cation have a greater proportion of the phosphate 

 of lime in their composition than is found in 

 the osseous system of the mammalia, and they 

 are whiter than the bones of any other animal. 

 In the bones where the medulla is not dis- 

 placed or dessicated by the extension of the 

 air-cells into their interior, the colour is of a 

 duller white. In the Silk or Negro-fowl of 

 the Cape de Verd Islands (Callus Murio, 

 Temminck) the periosteal covering of the 

 bones is of a dark brown, and in some parts 

 almost black colour ; but this ought to be re- 

 garded as a peculiarity of the cellular rather 

 than of the osseous texture, which does not 

 differ in colour from that of other birds ; 

 indeed the thin aponeurosis covering the lateral 

 tendons of the gizzard of the Silk-fowl is 

 observed to have the same dark hue as the 

 membrane which invests the bones. 



Although in the disposition of the parts of 

 the osseous system of birds the plan which 

 pervades the vertebrate type of structure is 

 nowhere absolutely violated, yet the variations 

 from that plan required by the peculiar exigen- 

 cies of the class are of the most striking and 

 interesting kind. We shall successively con- 

 sider the relations of these modifications to 

 the powers and habits of the bird as they 

 present themselves in the vertebral axis, in the 

 bones of the head and thorax, and in those 

 of the anterior and posterior extremities. 



Fig. 125. 



Skeleton of the Topaz Humming Bird ( Trochihu PeUti, 



The vertebral axis or spine is divisible into a 

 cervical (Jig. 125, ), dorsal (b), sacral (c), and 

 cintdal (d) region ; the vertebrae immediately 

 succeeding those which bear ribs have a lateral 

 anchylosis with the iliac bones, and therefore 

 there is no part of the spine which possesses 

 the characters of the lumbar vertebra of mam- 

 malia and reptiles. 



The vertebrae are the first parts of the osseous 

 system which make their appearance in the 

 development of the embryo, and they are of 

 all parts of the skeleton the most constant in 

 their existence and general characters. 



The dorsal or costal vertebrae in birds rarely 

 form more than a fourth part of the entire 

 vertebral column, and in some of the long- 

 necked Grallatores, as the Stork, form only 

 an eighth part of the spine ; they have not 

 been observed to be fewer than six nor more 

 than eleven in number throughout the class : 

 the latter obtains in the Swans (Ci/gnus canorus 

 et olor) and Sheldrake ; the most common 

 numbers are seven or eight. 



The dorsal vertebra? are short, as compared 

 with the cervical : they appear broad when 

 viewed superiorly, in consequence of the great 

 development of the transverse processes ; but 

 their bodies are much compressed in the lateral 

 direction, so as to be reduced almost to the 

 form of vertical laminae towards the sacral 

 region. This is especially observable in the 

 Penguins ( Aptenodytes, Catarrhactes) ; but 

 in the Ostrich the bodies of the dorsal ver- 

 tebras retain their breadth throughout. 



The bodies are not united by intervertebral 

 substances, but by capsular ligaments and 

 synovial membranes ; the anterior articular 

 cartilaginous surface is convex in the vertical 

 direction, and concave in the transverse ; the 

 posterior surface is the reverse. The Penguins, 

 however, present a remarkable exception to 

 this rule. The posterior surface of the third 

 dorsal vertebra is uniformly concave, to which 

 the opposed end of the fourth vertebra presents 

 a corresponding convexity : the ball and socket 

 joint is continued between the several ver- 

 tebras to the last dorsal, which is anchy- 

 losed to the sacrum. This is an interesting 

 affinity to the Reptilia, in addition to numerous 

 others displayed in the construction of these 

 singular birds. In most birds the bodies of 

 some of the middle dorsal vertebras are an- 

 chylosed together ; and in general those which 

 are nearest the sacrum. In the Flamingo we 

 have observed this anchylosis extending from 

 the second - to the fifth 

 dorsal vertebra. In the 

 Sparrow-hawk the second, 

 third, fourth, and fifth 

 dorsal vertebrae are conso- 

 lidated into one piece, 

 while the sixth enjoys con- 

 siderable lateral motion 

 both upon the fifth and 

 seventh, which last is an- 

 chylosed to the sacrum ; 

 so that the body can be 

 rapidly and extensively in- 

 flected towards either side 





