430 



In this portion of the oesophagus muscles are absent; 

 but in the pharynx and the anterior part of the oesophagus 

 these are well developed (fig. 124). There are the great 

 pharyngeal dilator muscles, whose structure and development 

 are described in connection with the general muscular system. 

 They are attached by one end to the front walls of the head, 

 and behind are inserted upon the epithelium of the front 

 walls of the pharynx. Their contraction serves to dilate the 

 pharynx. 



Attached to the hind wall are a number of other less 

 powerful muscles, which pass upwards and backwards and are 

 inserted upon the epithelium of the chitinous thickening on 

 the lower side of the oesophagus, above described. 



Besides these muscles there are a number of others, much 

 shorter than these, which are distributed longitudinally and 

 circularly on the intestine. The longitudinal muscles are 

 long spindle-shaped structures forming three or four layers 

 on the front of the pharynx; on the oesophagus they are 

 much more scanty. The circular muscles are arranged on the 

 pharynx in thick bundles, lying outside the longitudinal 

 muscles, each bundle being inserted upon the two lateral 

 walls of the pharynx, which they partly enclose like a crescent. 

 The circular muscles of the oesophagus are thin plates, not 

 arranged in thickened bundles. 



These bundles are all of the "striated" type. The 

 oesophageal muscles appear to be unicellular. The longi- 

 tudinal muscles of the pharynx are composed of five to six 

 cells, fused into a syncytium. 



The crop is a curious structure (fig. 159) ; its walls consist 

 of very flat paper-like cells, in which cytoplasm is very much 

 reduced. They closely resemble the cells of the wing epi- 

 thelium before this straightens out on emergence, but always 

 retain their nucleus and a very small amount of cjrtoplasm. 

 Within their walls lie very fine muscles, which also serve to 

 connect them with the crop. 



-"^ These muscles are of a type which has not, so far as I 

 am aware, been observed hitherto (fig. 125). They contain 

 a small nucleus, which lies as a thickening on the fine hair- 

 like muscle. But the muscle itself is not of the usual compact 

 type, but possesses several branches, which may run in various 

 directions; each branch represents one, or, at any rate, a very 

 small number of fibrillae, and presents the usual striations. 

 The fibrillae are too limited in number, however, for the 

 striations to be able to dispose themselves in spirals, and for 

 once it is possible to speak of true transverse striation. 



The gizzard, on the other hand, is a very powerful organ. 

 It measures only 70/a in length, 40/x in thickness. In shape 



