SO MORPHOLOGY OF THE VEBTEBRATA. 



SACRAL VERTEBRAE 



Are four in number, and are all anchylosed together. From their 

 several arches are prolonged horozontal tranverse processes, which 

 are flattened from above downwards, and unite with the ilia. 

 The inferior surfaces of their centra are deeply concave, forming 

 deep fossae for the reception of the middle lobes of the kidneys. 



CAUDAL VERTEBRA. 



The anterior of these have lamellar transverse processes. The 

 three first possess ribs, which are anchylosed at their proximal 

 extremities with both the centra and neural arches of their 

 vertebrae, while at their distal expanded ends they abut against 

 the ilium. The anchylosed caudal vertebrae are distinguished by 

 the name urosacral. The succeeding caudal vertebrae are 

 numerous and free, except the most posterior, which are 

 anchylosed into a ploughshare-like bone — named the pygostyle — 

 which supports the so-called preening gland and the quill feathers 

 of the tail (restrices). It is set on the spine, at a nearly vertical 

 angle with the axis of the body. 



The bodies of the cervical and of those dorsal vertebrae which 

 are moveable are connected to one another by means of fibro- 

 cartilaginous rings, which extend from the circumference of the 

 one to that of the other. Each ring is prolonged in between two 

 contiguous centra into a disc — the meniscus — which is free on both 

 its anterior and posterior surfaces. This meniscus is perforated 

 at its centre. In this manner the synovial space between any 

 two centra becomes separated into two narrow compartments, 

 •communicating with one another by the perforation in the 

 meniscus. In the caudal region, however, the meniscus is united 

 with the faces of the centra of the vertebrae, and so resembles an 

 intervertebral cartilage — like that of man. 



THE RIBS 



Are flexible arches of bone, which wall in the thoracic cavity 



below. They are seven in number on either side — each dorsal 



vertebrae having a rib attached to it. The third, fourth, fifth, and 



.sixth are connected above with the spine, and below with the 



sternum, through the intervention of the sternal ribs. The first 



two are free ribs — that is, they have no connection with the 



sternum. The ribs are situated one behind the other, in such a 



way that spaces are formed between them, which are named the 



intercostal spaces. They increase in size from the first to the 



sixth. 



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