286 GENERAL ORNITHOLOGY part ii 



under control of the will, as that of the heart. This species is 

 usually of a rich red colour (pale pink in many birds of the grouse 

 family), and is the ordinary " flesh " of the body. The other 

 species, M. Icevis, composes the pale or colourless smooth fibre of 

 the involuntary muscles, as those of the intestines, the gullet, etc. 

 A species of contractile tissue commonly referred to the genus 

 Desmammha (indifferent connective-tissue cells) is very near My- 

 amceba Icevis; example, mammalian dartos. The movements of 

 erectile organs, as the neat combs over the eyes of grouse, or the 

 turkey's caruncles, are not in any sense myamcebic, but depend 

 mechanically upon influx of blood. 



The Muscular System of Aves can only be touched upon ; it is 

 impossible in my limits to even name all the muscles, much less 

 describe them. I can only note the leading peculiarities, and pre- 

 sent a figure in which the principal muscles are named. 



The subcutaneous sheet of muscle (of which the human " muscles 

 of expression " and platysma myoides are segregations) is broken up 

 in birds into a countless number of little slips which agitate the 

 feathers collectively, and especially the great quills of the wings 

 and tail. There are estimated to be 12,000 in a goose. The 

 prime peculiarity of birds' musculation is the enormous develop- 

 ment of the pectorales, or breast muscles, which operate the wings. 

 The great pectoral, p. major or p. primus, arises from the sternal 

 keel, when that special bony septum between the fellow-pectorals 

 exists, and from more or less of the body of the sternum, passing 

 directly to the great pectoral or outer ridge of the humerus, near 

 the upper end of that bone. Its origin may even exceed the limits 

 of the sternum, invading the clavicle, etc. ; it may unite with its 

 fellow. It is the depressor of the humerus, giving the downward 

 stroke of the wing. The next pectoral, p. secundus or p. medim, 

 arises from much or most of the sternum not occupied by the first, 

 under cover of which it lies ; it passes also the humerus, but by an 

 interesting way it has of running through a pulley at the shoulder 

 it elevates that bone, giving the upward wing-stroke. A third 

 pectoral, p. tertius or p. minimus, arising from sternum, and often 

 contiguous parts of the coracoid bone, passes directly to the hume- 

 rus, supplementing the action of the first. A fourth muscle in 

 many birds acts upon the humerus from the sternum or coracoid, 

 particularly the latter. These four differ greatly in their relative 

 development. Such extent of the sternum and pectoral muscles 

 correspondingly reduces that of the belly-walls, and the abdominal 

 muscles are consequently scanty. Fixity of the spinal column in 

 the dorsal region diminishes the musculation of that part, the spinal 

 muscles being much better developed in the cervical region ; where, 

 in cases of some of the long-necked birds, there are curious con- 



