272 



AVES. 



water it is in general remarkably elongated, 

 whether they support themselves on the surface 

 by means of short and strong natatory feet, as 

 in the Swan, or wade into rivers and marshes 

 on elevated stilts, as in the Crane, &c. 



The articular surfaces of the bodies of the 

 cervical vertebrae, like those of the -dorsal series 

 above mentioned, are concave in one direction 

 and convex in the other, so as to lock into each 

 other, and in such a manner that the superior 

 vertebra move more freely forwards, the middle 

 ones backwards, while the inferior ones again 

 bend forwards ; producing the ordinary sigmoid 

 curve observable in the neck of the bird. 



This mechanism is most readily seen in the 

 long-necked waders which live on fish and 

 seize their prey by darting the bill with sudden 

 velocity into the water. In the common Heron, 

 for example, (Ardea cinerea) the head can be 

 bent forward on the atlas or first vertebra, the 

 first upon the second in the same direction, 

 and so on to the sixth, between which and 

 the fifth the forward inflection is the greatest ; 

 while in the opposite direction these vertebrae 

 can only be brought into a straight line. From 

 the sixth cervical vertebra to the thirteenth the 

 neck can only be bent backwards ; while in 

 the opposite direction it is also arrested at a 

 straight line. From the fourteenth to the 

 eighteenth the articular surfaces again allow 

 of the forward inflection, but also limit the 

 opposite motion to the straight line. 



Two transverse processes are ordinarily con- 

 tinued from the anterior part of the bodies of 

 the cervical vertebrae : the inter-space of these 

 is filled up externally to the vertebral artery 

 by a rudimentary styliform rib, which is sepa- 

 rated in the young bird, but afterwards ancliy- 

 losed, and directed backwards parallel to the 

 body of the vertebrae. These processes give 

 attachment to numerous muscles of the neck, 

 and being, with the transverse processes, more 

 strongly developed in the rapacious birds, give 

 a greater breadth to the cervical region in that 

 order. 



The superior spinous processes are but 

 feebly developed ; they are most distinct on 

 the vertebrae at the two extremities of the 

 cervical portion of the spine. Inferior spinous 

 processes are also found on the vertebrae at 

 the commencement and termination of the 

 neck, but are wanting in a great proportion of 

 the intermediate cervical vertebrae. 



The atlas is a simple ring. In general it 

 is articulated with the occipital tubercle by 

 a single concave facet on the body ; but in 

 the Penguin and Ostrich there are two other 

 facets, continuous with the middle one, but 

 corresponding with the anterior articulating pro- 

 cesses of the rest of the vertebrae and applied to 

 the condyloid portions of the occipital bone, 

 while the middle facet is articulated to the ba- 

 silar portion as in other birds. The body of 

 the dentata is joined to the atlas by a single 

 synovial capsule, its odontoid process is tied 

 down by a strong transverse ligament stretched 

 above it, and by a longitudinal one extending 

 from its extremity to the posterior part of the 

 occipital condyle. In the articulations of the 



bodies of the remaining cervical vertebrae a 

 moveable inter-articular cartilage is found in- 

 closed between reduplications of the synovial 

 membrane, as in the joint of the lower jaw in 

 mammalia. The articulations of the oblique 

 processes have no peculiarities worthy of no- 

 tice. 



A remarkable difference is found in the 

 diameter of the spinal canal contained in the 

 cervical vertebrae. If, e. g. the sixth cervical 

 vertebra of a Stork be sawed down verti- 

 cally, the antero-posterior diameter is greatest 

 in the middle, least at the ends ; but if it be 

 sawed lengthwise horizontally, the transverse 

 diameter is the reverse, being narrowest at 

 the centre and widest at the ends. In the 

 Ostrich, the Swan, and many other birds the 

 spinal canal is widened in every direction at 

 the extremities of the vertebrae ; and on the dor- 

 sal or posterior aspect of the spine, the canal 

 remains open for some extent in the intervals of 

 the vertebrae, the cord being there protected 

 only by membrane and the elastic ligaments 

 which connect the roots of the spinous pro- 

 cesses together. The final purpose of this 

 structure has been ably illustrated by Mr. Earle 

 in the Philosophical Transactions, (1822, p. 

 276.) where he shews that it is adapted to pre- 

 vent a compression of the spinal cord during 

 the varied and extensive inflections of the neck. 



The vertebrae of the different regions of the 

 spine bear a different proportion to each other 

 in respect to number among birds, from what 

 we observe in the mammalia and reptilia. The 

 cervical portion in this class is generally com- 

 posed of a much greater number of vertebrae 

 than any of the other divisions of the spine ; 

 in this respect the fossil reptilian genus called 

 Plesiosaurus alone resembles the bird. This 

 singular animal was an inhabitant of the 

 waters, and it is interesting to observe that 

 the peculiarity which distinguishes it, viz. the 

 great length of neck, is chiefly characteristic 

 of the Aves aquatics of Nitzsch. In the Gral- 

 latores the length of the neck is determined by 

 the height of the legs : in the Natatores it is 

 necessary for the purpose of obtaining their 

 food while swimming the waters. The dorsal 

 vertebrae are usually less numerous than in 

 mammalia. The caudal vertebrae are subject 

 to few variations; they never project in the 

 form of a tail, but are most numerous in those 

 birds which make the greatest use of the tail- 

 feathers, as in the Swallows, to direct their 

 rapid flight, and in the Woodpeckers, where 

 they serve as a prop or climbing pole. 



The following table, which, with some cor- 

 rections, is extracted from Cuvier's Lefons 

 d'Anatomie Comparee, exhibits the variety 

 that exists with respect to the number of ver- 

 tebrae in different species of birds. 



Table of the number of vertebra in birds. 



Order. RAPTORES Vertebra. 



Species. Cervical. Dorsal. Sacral. Caudal. 



Vulture 13 7 11 7 



Eagle 13 8 11 8 



Osprey 14 8 11 



Sparrow-hawk.. 11 8 11 8 



