206 THE ANATOMY OF VERTEBRATED ANIMALS. 



cumscribed patches or bands, between which the integument 

 is either bare, or covered only with down. These series of 

 contour feathers are termed ^feryto, and their interspaces, 

 aj^teria. 



In some birds, such as the Herons, plumulee of a peculiar 

 kind, the summits of which break off into a fine dust, or pow- 

 der, -as fast as they are formed, are developed upon certain 

 portions of the integument, which are termed powder down 

 patches. 



The integument of birds is, for the most part, devoid of 

 glands ; but many birds have a peculiar sebaceous gland 

 developed in the integument which covers the coccyx. This 

 uropygial gland secretes an oily fluid, which the bird spreads 

 over its feathers by the operation of "preening." The excre- 

 tion passes out by one or two apertures, commonly situated 

 upon an elevation, which may or may not be provided with a 

 special circlet of feathers. 



In various birds (e. g., the Turkey) the integument about 

 the head and neck develops highlj'-vascular and sometimes 

 erectile processes (combs, wattles). 



The spinal column of birds contains numerous and well- 

 ossified vertebrae, a considerable number of which (more than 

 six) are anohylosed together to form a sacrum. Of the verte- 

 br£e which enter into the composition of this complex bone, 

 however, not more than from three to five can be regarded as 

 the homologues of the sacral vertebrae of a Crocodilian or 

 Laoertilian reptile. The rest are borrowed, in front, from the 

 lumbar and dorsal regions ; behind, from the tail. The cervi- 

 cal region of the spine is always long, and its vertebrae, which 

 are never fewer than eight, and may be as many as twenty- 

 three, are, for the most part, large in proportion to those of 

 the rest of the body. 



The atlas is a relatively small ring-like bone ; and the 

 transverse ligament may become ossified and divide its aper- 

 ture into two — an upper, for the spinal cord, and a lower for the 

 odontoid process of the axis vertebra. The os odontoideum 

 is always anchjdosed with the second vertebra, and constitutes 

 a peg-like odontoid process. 



The spines of the succeeding cervical vertebrfe are often 

 obsolete, and are never very prominent in the middle region 

 of the neck. The anterior faces of their elongated vertebral 

 centra are oylindroidal, slightly excavated from above down- 

 ward, and convex from side to side ; while the posterior faces 



