OF COLYMBUS TORQUATUS. 143 



is semilunar in shape, and very deep. Its concave inner border is formed to a considerable 

 extent by ligaments, which separate it from the depression in which lodges the odontoid 

 process of the axis, and serve to increase the depth of both these depressions. The body 

 of the bone is, on the ventral aspect, prolonged as a spine of inconsiderable size, — the 

 commencement of the ventral series of processes. 



Dorsal vertebrce. If we consider the dorsal vertebrae as corresponding in number with 

 the ribs, we should assign ten to this portion of the spinal column. The last three ribs, how- 

 ever, correspond to vertebrae which are completely anchylosed to the sacrum as well as to 

 the iliac bones, and at the same time they differ in several respects from the dorsal ribs 

 proper. It seems more natural, therefore, to consider these ribs as really appertaining to 

 the sacrum, leaving seven to be viewed as true dorsal ribs, — and consequently to con- 

 sider the number of dorsal vertebrae to be the same. 



The transverse processes of these vertebrae are as usual very broad, long, and thin; their 

 posterior borders concave, their anterior convex, and their postero-external angles pro- 

 longed backwards into a short " styliform " process, more or less intimately connected 

 with the next succeeding vertebra. The horizontal lamellae of the transverse processes of 

 the last four vertebrae are pierced by a quite large foramen. 



The superior spinous processes of the vertebrae are so long that they nearly touch 

 each other by their anterior and posterior borders ; only a slight space being left between 

 them. They are quite regularly rectangular in shape, having straight flat superior borders 

 at right angles with the anterior and posterior borders. They are connected with each 

 other by dense and strong ligaments, and probably become more or less completely an- 

 chylosed with age. 



The bodies of the dorsal vertebrae present the usual feature of being exceedingly com- 

 pressed, until they are almost vertical laminae of bone. But the most interesting feature 

 of this portion of the spinal column is found in the enormous development of the inferior 

 or ventral spinous processes. As the bird must be enabled to dart its neck forward with 

 great power and rapidity, in the capture of its prey, we find these processes, which are the 

 points of origin of the powerful longi colli, developed to a corresponding degree. The 

 first ventral process consists of two broad thin laminae of bone projecting downwards and 

 outwards on either side, divided by a median ridge. These laminae are sessile on the body 

 of the vertebra. The second, third, and fourth are more peculiar. A compressed pedicle of 

 a length increasing from before backwards, shoots down from the ventral aspect of the body 

 of the vertebra, and bears upon its summit two broad, thin, flat lamellae of bone, which, 

 divaricating from each other at a very obtuse angle, expand outwards and downwards. 

 These alae are largest upon the third dorsal vertebra. Upon the fourth they are smaller; 

 and on the fifth, sixth, and seventh become almost atrophied, although the pedicle retains its 

 length. The pedicle of the fifth vertebra is the longest. These ventral processes are well 

 developed on the first sacral vertebra, are merely a minute projection on the second, and 

 totally disappear on the third. 



The movements of this portion of the spinal column are exceedingly restricted, and 

 if any exist, they are in a lateral direction. The last cervical vertebra is very freely 

 movable in all directions upon the first dorsal. The last dorsal and first sacral have 

 also perfect articulating facets ; but their spinous processes are so extensively anchylosed, 

 that it is probable that but little motion exists between those portions of the spinal 

 column. 



JIKMOIES BOST. SOC. NAT. HIST. Vol. I. Pt. 2. 37 



