MOVEMENTS OF THE EN 7 TEROPNEUSTA. 259 



dorsal half of the body in these regions. Ventral curvature as 

 well as fore-and-aft shortening is consequently a general result 

 of the contraction of these muscles. 



The chief interest in the myology of the animal centers in the 

 collar and peduncle. Here we have no dermo-muscular tube, 

 but, on the contrary, a musculature of a fundamentally different 

 type. The muscles, both longitudinal and circular, of the dermo- 

 muscular tube are always, it will be recalled, strictly somatic, 

 i. c., they belong to the body wall. The chief mass of muscles 

 of the collar and peduncle, viz., the radio-longitudinal muscles, 

 while attached to the body wall at one end, at the other are on 

 the other hand attached to the notochord and nuchal skeleton 

 mainly, but partly also to the wall of the esophagus. 



The full details of the origin, insertion, and relations of these 

 large muscles are too complicated to admit of being fully set 

 forth otherwise than by an elaborate, well-illustrated description ; 

 but an understanding of the most important facts may be given by 

 a brief presentation, particularly if reference be made to Spengel's 

 monograph. Figures n, PL 14, and 20, 28, 32 and 34, PI. 15, 

 Imi. marking the muscles under consideration, are especially 

 clear and instructive in this connection. 



The two muscle masses are bilaterally situated and are in gen- 

 eral coextensive in length with the collar and peduncle together. 

 Their origins are on the sides of the combined notochord and 

 nuchal skeleton anteriorly, /. c., in the peduncle ; and on the 

 esophageal notochord and esophagus itself posteriorly, i. c., in 

 the collar (compare Figs. 4 and 7, i. 1. c. in., PI. VII., of the 

 author's paper on Harrimania maculosa 1 }. 



From these extensive origins the fibers extend backwards and 

 outwards, some to become inserted into the outer edges of the 

 septum separating the thoracic and collar cceloms ; some, with a 

 more oblique course, to insert into the ectoderm or the under- 

 lying connective tissue, along the postero -lateral portions of the 

 collar ; and still others at the anterior end of the collar, with a 

 course predominantly radial, to insert into the ectoderm of the 



1 Papers from the Harriman Alaska Expedition, II. Harrimania macttlosa, a new 

 genus and species, etc. Proc. Wash. Acad. of Sciences, Vol. II., Aug. 20, 1900, 

 p. III. 



