COCCYGEAL VERTEBRA 



373 



the superior has a set of strong ligamentous fibres similarly attached. 

 The base looking forwards has been already described as consisting of three 

 articular surfaces, above which is the spinal foramen. The apex is only 

 marked by the surface of articulation with the first bone of the coccyx, 

 above which is the spinal foramen, here obliquely cut and small, and pre- 

 senting also the rudiments of oblique and transverse processes. 



THE COCCYGEAL VERTEBRAE 



These bones form the skeleton or bony basis of the tail, receiving their 

 name fi-om kokkv^, a cuckoo, whose bill was supposed to resemble this part in 

 the human body. They vary in number from sixteen to eighteen. In the 



(S^ 



C^4 



Fig. 20. — Profile View of Coccygeal Vertebr^e. 



1. 1. 1. etc. Bodies. 3. 3. 3. Transverse processes. 



2. 2. 2. Spines ; the lips forming the first are 4. 4. 4. etc. Fore surfaces by means of which th» 



joined, forming the neural arch, the second bodies articulate, 



partially so, and the third are open. 5. 5. 5. Bacli surfaces of articulation. 



A, first ; B, third ; C, eighth ; D, sixteenth ; E, seventeenth ; P, eigliteenth, or last coccygeal vertebra. 



first four or five all the characters of a vertebra are present, as shown below 

 at A B ; but these are gradually lost, and the bones at last assume the form 

 of simple spines, d e f, the intermediate grade being seen at c. Here there 

 are two little processes (2), evidently abortive neural arches or lateral 

 laminse, but not meeting together to form the spine. This whole set of 

 bones is simply intended as a strong and flexible whip, to be moved by the 

 four sets of muscles lying along, and attached to the sides of each. 



THE RIBS AND THEIR CARTILAGES 



The eibs (costce) have been described at page 351 as forming the lateral 

 boundaries of the thorax. They are eighteen in number, of which the nine 

 anterior (true or sternal) extend by means of their cartilages to the sternum, 

 while the cartilages of the remainder do not extend so far, and they are 

 therefore styled false or asternal (see Skeleton at page 348). 



The ribs are all long flattened bones, irregularly twisted on themselves, 

 and so arranged that, when forming the walls of the thorax, they readily 

 increase the volume of its contents by being drawn nearer together and 

 towards the apex. In doing this they revolve upon their extremities aa 

 upon two centres, the superior admitting of motion from their formation aa 

 joints, and the inferior from their elastic cartilaginous structure. 



