MUSCULAR SYSTEM. 83 



tensively developed in the present class, as also the muscles which 

 bristle up the feathers upon the neck and head particularly of those 

 birds, where they arise in tufts. In the Gallinse a peculiar tegu- 

 mentary muscle supports the crop as it hangs down in the neck. 

 The strongest, tegumentary muscles occur in the Apteryx, in which 

 several distinct layers and fasciculi may be distinguished ; a pro- 

 vision very necessary to this bird, which scratches deep in the earth, 

 and must therefore shake its feathers with considerable force to 

 dislodge the dirt from them. In addition to these muscles in birds, 

 there are strips appropriated to the feathers, which becoming de- 

 tached from the tegumentary muscles, form a sheath around the 

 quill part of each feather where it projects into the skin. They 

 are wanting generally to the down-feathers, and are in the others 

 easily overlooked on account of their small size in most birds. In 

 the larger birds, however, as some of the Palmipedes, c. g. the 

 Pelican, Goose, and Duck, they are very much developed, each 

 feather receiving four, more rarely five, small muscular fasciculi, 

 which can move the feather in all directions, so that in Sula and 

 Anas, where about 3,000 quill-feathers are reckoned upon the body, 

 the number of these muscles amounts to 12,000. The muscles of the 

 great primaries of the wing are the largest. No muscles are found 

 upon the face of birds, the greatest part of which is covered by 

 horny substance. The temporal, masseteric and pterygoid muscles, 

 as well as the depressor of the lower mandible, are strongly devel- 

 oped, and so arranged, that in acting, they effect at the same time 

 the movement of the upper maxillary arch and tympanic bones. It 

 is rare for an asymmetrical disposition of these muscles to occur, as 

 in the singular cross-bill of the Loxia curvirostra, in which the mus- 

 cles of the jaws are more strongly developed upon one side than the 

 other, but always upon that toward which the apex of the lower jaw 

 is turned up in a stale of rest. 



As might be anticipated from the great degree of motion and 

 flexibility of the neck, and the consequent freedom with which the 

 head can be turned in all directions, the muscles of the neck and 

 its nape exhibit numerous subdivisions, and are powerfully developed. 

 The neck, especially when long, can be contorted like the body of a 

 serpent in the most varied manner, a condition which was essen- 

 tial to birds, from their jaws having to serve principally as instru- 

 ments of prehension. The fixed and partly anchylosed condition 

 of the vertebrae of the trunk afford a strong immoveable point of 

 attachment to part of the cervical muscles ; while the muscles of 



