MONOGRAPH OF THE EXISTING CRINOIDS. 339 



In the ground substance of the skeleton adjacent to the attaching plates of 

 the muscle fibers Reichensperger found peculiar crescentic or semicircular cells 

 with large, deeply staining nuclei, which give off from the two ends complicated 

 ramifying processes running fiber-like in various directions, some of which accom- 

 pany the muscle fibers for a short distance. 



Reichensperger believes that these may be specially differentiated connective 

 tissue elements which aid in strengthening the part to which the muscles are 

 attached. They have nothing to do with the innervation of the musculature, which 

 is accomplished by a ventral branch from the axial cord that in the form of 

 extremelv fine twigs penetrates the muscle bundle from the side and runs up on 

 the fibers. 



Muscle fibers similar to those just described occur in Isocrinus and in the 

 Comasteridse. 



EPITHELIAL MUSCLES. 



In the walls of all the water vessels very numerous muscle fibers are found, 

 most of which run parallel to the axis of the vessels, a few traversing the lumen. 

 These are connected with the epithelial cells lining the water vascular canals. 



The true epithelial cells are cubical; but connected with each of them and 

 running longitudinally along the wall of the canals or across the lumen is a short 

 spindle-shaped muscle fiber, terminally pointed, which in Antedon mediterranea 

 measures from 0.02 mm. to 0.03 mm. in length, but scarcely half of that if strongly 

 contracted. 



LIGAMENTS. 



The so-called ligaments uniting the pinnulars and cirrals, occupying the inter- 

 articular and dorsal ligament fossse of the muscular articulations, as well as the 

 paired fossae of the synarthries, binding the syzygial surfaces together, and in 

 the stalked crinoids uniting the columnals, are all of the same nature. In the 

 muscular articulations a differentiation has usually been made between the liga- 

 ments occupying the interarticular ligament fossse and the ligament pit in the 

 dorsal ligament fossa, and those of the rest of the dorsal ligament mass; but this 

 division can not be maintained histologically. 



In life the dorsal ligament mass is white and glistening, and the interarticular 

 ligament masses in reflected light are bluish with a marked mother-of-pearl luster. 



The interarticular ligament masses are much tougher than the others, and 

 resist the action of caustic longest. 



The fibers of the dorsal ligament are almost always bowed outward, away 

 from the axis of the arm. 



In the interarticular ligaments the individual fibers are much more slender 

 and noticeably shorter than those in the dorsal ligament. Stout and slender fibers 

 are here intermingled so that a felt-like appearance is produced. 



Jickeli was the first to indicate that the so-called ligaments between the 

 cirrals are not of a purely elastic nature. He had noticed that the cirri are capable 

 of active movement. 



