n-] THE SPINAL SKELETON. 67 



divided into a median and two lateral processes, one on each 

 side (as in the Apteryx) ; or into a median process and four 

 lateral ones there being an internal and external xiphoid 

 process on each side of the median one as in very many 

 birds (^.gallinaceous birds, such as the Fowl and Pheasant). 

 This median process it is which bears the keel, or the greater 

 part of the keel, in Birds. 



FIG. 77. THORAX OF A GALLINACEOUS BIRD. 



ft, keel of entro-sternum ; in, middle xiphoid process ; i, intermediate xiphoid 

 process ; e, external xiphoid process ; r, rostrum ; c, costal process ; k, hypa- 

 pophysis ; a, appendage from ribs, or uncinate process. 



In certain animals (e.g. the Monotremes) there is a median 

 ossicle in front of the manubrium, which is often called the 

 episternum. This really forms part of the appendicular 

 skeleton, being a portion of the shoulder structure. It will 

 therefore be noticed under that head. 



35. In possessing RIBS (that is, distinct osseous or cartila- 

 ginous parts attached at one end to the vertebral column, and 

 tending to surround the body cavity) man agrees with the 

 immense majority of other Vertebrates. Some, however, as 

 the Frogs and Toads, have none, nor can any be said to exist 

 in some of the lowest Fishes, e.g. the Lamprey and its allies. 



In the division of the ribs into two categories, the "true" 

 and the "false" ribs, man agrees with all animals which have 

 ribs at all, except Serpents, Fishes, and Chelonians ; Serpents 

 F ? 



