AVES. 



271 



during the pursuit of prey. This structure 

 and its uses were first pointed out by Mr. 

 H. Earle. 



The bodies of the anterior dorsal vertebrae 

 send down processes from their inferior or 

 ventral surfaces for the advantageous origin 

 of the recti ant id majores muscles of the neck. 

 These processes differ from the inferior spines 

 of the tail in not being perforated for the 

 passage of an artery. This part of the spine 

 is further strengthened by the extension of 

 osseous splints from the transverse processes, 

 which unite those of contiguous vertebra; to- 

 gether, and also by the anchylosis of the 

 spinous processes. But where a similar ne- 

 cessity for the fixation of the trunk does not 

 exist, as in the Struthious birds and Penguins, 

 which cannot fly, all the dorsal vertebrae are 

 moveable upon each other. When it is con- 

 sidered that the head, posterior extremities, 

 and viscera are suspended in flight from this 

 central portion of the trunk, and that it has 

 almost exclusively to sustain the shock of the 

 violent contractions of the principal muscles 

 of the wings, the necessity for the mechanism 

 consolidating the dorsal vertebrae will be readily 

 appreciated. 



Immobility and strength are still more ob- 

 viously required in that part of the spine by 

 which the weight of a horizontal body is to 

 be transferred to a single pair of extremities 

 articulated to the trunk behind the centre 

 of gravity. The anchylosis of the bodies of 

 the vertebra?, which already begins to appear 

 in the last dorsal, is, therefore, continued 

 through all the sacral vertebrae as far as the 

 caudal region; and this consolidated mass 

 (b to c) is united laterally to the iliac bones. 

 Hence it is always difficult to determine the 

 number of vertebrae of which it is composed. 

 We have made sections of the sacrums of many 

 different birds with a view to determine this 

 fact, and have generally found the number 

 greater than that which is indicated in the 

 tables of Cuvier. Thus the Stork has twelve, 

 instead of eleven sacral vertebrae ; the Coot 

 thirteen, instead of seven ; the Kingfisher 

 eleven, instead of eight : while the Ostrich, on 

 the other hand, has but seventeen, instead of 

 twenty bones of the sacrum. The bodies of 

 the sacral vertebrae are broad, but shallow, and 

 towards the tail the floor of the vertebral canal 

 is formed by a mere lamina of bone : the canal 

 is remarkably dilated in this part of the spine 

 for the enlargement of the cord which gives 

 off the nerves to the posterior extremity. It 

 is a curious fact that the roots of these nerves 

 pass out of the osseous canal by separate 

 orifices, the ganglion on the posterior root 

 and the union of the two being external to the 

 spine. The aspect of all these orifices is la- 

 teral, in the intervals of the transverse pro- 

 cesses of the different vertebra, which are not 

 united together as in the mammalia. The first 

 four or five sacral vertebrae give off two sets 

 of transverse processes, one ventral, the other 

 dorsal ; the ventral ones are wanting in the 

 succeeding four, and then suddenly reappear 

 to abut against the symphysis of the ilium and 



ischium, and arc so continued double to the 

 end. The spinous processes which are prin- 

 cipally developed from the anterior sacral ver- 

 tebra;, give off from their extremities lateral 

 expansions, which anchylose with the iliac 

 bones, and form an osseous roof, arching over 

 and concealing the transverse processes. 



The coccygeal vertebrae of birds, though never 

 prolonged into a conspicuous caudal appen- 

 dage, are in general moveable upon each other, 

 and are frequently nine in number. With the 

 exception of the last, they are broad and short 

 and perforated for the lodgement of the spinal 

 marrow. With the exception of the last also 

 they have spines on both the dorsal and ventral 

 aspects ; and the anterior vertebrae have also 

 transverse processes. The last caudal vertebra 

 (d, Jig. 125) is so singularly shaped, that were 

 it found alone in a fossil state it would hardly 

 be recognized as a bone of the spine. It has 

 no medullary canal and no processes ; but is 

 compressed laterally and terminates above and 

 often also below in a sharp edge ; its posterior 

 extremity is obtuse. It supports the coccygeal 

 oil-gland, and affords a firm basis to the tail 

 feathers, which, from their use in guiding the 

 motions of the bird through the air, Linnaeus 

 termed the rectrices.* 



In the Toucan the three last caudal vertebrae 

 are anchylosed together ; the six anterior ones 

 are articulated by ball and socket joints, the 

 ball and the socket being most distinct in 

 the two last of these joints ; that between the 

 sixth and seventh vertebrae is provided with a 

 capsule and synovial fluid, the others have 

 a yielding ligamentous mode of connexion. 

 The spinous processes of these vertebrae, both 

 superior and inferior, are of moderate size, but 

 smallest in the sixth, where the greatest degree 

 of motion takes place ; the transverse pro- 

 cesses on the contrary are large and broad 

 so as almost to preclude lateral motion. We 

 have given a more particular description of 

 these vertebrae because of the singular move- 

 ments observable in the tail of the Toucan ; 

 it can be inflected dorsad till the superior 

 spines of the vertebrae are brought in contact 

 with the sacrum ; and in the performance of 

 this motion the lateral muscles, which at first 

 tend rather to oppose the elevators, become, at 

 a certain point of inflection dorsad of the centre 

 of motion, elevators themselves, and thus com- 

 bining with the elevators jerk the tail upon the 

 back ; it is thus that the tail turns as if on a 

 hinge operated upon by a spring. 



As the prehensile functions of the hand are 

 transferred to the beak, so those of the arm 

 are performed by the neck of the bird; this 

 portion of the spine is therefore composed of 

 numerous, elongated, and freely moveable ver- 

 tebrae, and is never so short or so rigid but that 

 it can be made to apply the beak to the coccy- 

 geal oil-gland, and to every part of the body 

 for the purpose of oiling and cleansing the 

 plumage. In birds that seek their food in 



* In the tail-less variety of the common Fowl 

 the coccygeal vertebrae have degenerated into a 

 single unshapely knotty process. 



