MR. W. K. PARKER ON THE OSTEOLOGY OF BALyENICEPS REX. 327 



of which will soon be explained. The compression of the centrum of the third cervical 

 in Baleeniceps is very great, and towards its hinder part there is a blunt rudimentary 

 hypapophysis, marked below by three parallel lines. The fifth cervical of the Balae- 

 niceps begins to take on the normal shape of the vertebrae of the cervical region in birds : 

 the spine without being higher is more compressed than in the fourth ; the anterior 

 inter-spinous tubercle is vertical, whilst that behind the neural spine is, as in most of 

 the cervicals, very oblique. The centrum in this vertebra is thicker, having attained 

 the normal proportions ; but it is still convex beneath, and its anterior half is marked 

 by two nearly parallel ridges about two lines apart from each other. 



In this fifth vertebra, as well as in the fourth and the third, there is a pair of strong 

 bridges for the vertebral arteries. These bridges are completely closed by an undivided 

 bony ring to the fifteenth (inclusive), and they increase in size gradually ; those of the 

 third cervical being only a line and a half in diameter, whilst those of the fifteenth are 

 nearly four lines across. The spine of the sixth cervical in Baleeniceps is smaller than 

 that of the fifth, and these processes decrease regularly to the thirteenth ; but in the 

 fourteenth the neural spine is more evident, whilst in the fifteenth to the seventeenth 

 we have an approach to the condition of the process in the true dorsals. The inferior 

 surface of the sixth cervical is concave, and at its anterior end the parapophyses send 

 inwards a blunt process on each side, which processes, in the fresh state, are connected 

 together by inter-osseous membrane, thus forming a canal for the carotid arteries. 

 But in the seventh to the thirteenth (inclusive), these processes of the parapophyses meet 

 at the mid-hne (PI. LXVI. fig. .5 cc), at which part they are somewhat carinate externally, 

 whilst the passage itself is circular. The inferior margins of the centrums of these ver- 

 tebrae, with four perfect canals, are marked by a sharp and rather scabrous ridge ; between 

 these marginal ridges the inferior surface of the centrum is rather flat, whilst it is more 

 concave at each end. The concavity of the posterior third is formed by the swelling of 

 the bone both outwards and downwards, on each side, to form the posterior articular 

 facet. This lateral expansion leaves the bone scooped and concave at the mid-line, 

 thus exactly adapting it to the anterior end of the next succeeding vertebra. 



The principal pneumatic foramina enter the axis behind the upper transverse process, 

 or diapophysis, but in the rest of the spine to the last caudal, the largest pneumatic 

 openings are on the front face of these processes. The last carotid arch— that on the 

 thirteenth cervical — is marked beneath by two small sub-mesial keels. The last four 

 cervicals have no carotid arch or canal, but in their place there is, at the anterior end, 

 a rather thick, subquadrate azygous process (PI. LXVI. fig. 1 hp) ; that on the seven- 

 teenth, or last cervical, being the smallest, whilst that on the fifteenth is the largest, 

 being about five lines broad and four lines deep. These are, according to Professor^ 

 Owen, ' hypapophyses,' and the carotid canals, although formed by a pair of laminae, life' 

 considers to be of the same nature. 



From the thirteenth to the seventeenth cervical (inclusive) there is a much greater 



2 z 2 



