Clark — Origin of Crinoidal Muscular Articulations. 43 



difference being that the latter are extremely short. Now 

 since the fibers of the dorsal ligament and of the syzygy are 

 identical except in length, we should expect that they both 

 would possess the same physiological characteristics, and, there- 

 fore, that the fibers of the syzygy would be contractile in the 

 same way that those of the dorsal ligament are, though their 

 possible loss or gain in length, owing to their shortness, would 

 be very slight. As the fibers of the syzygy are continuous in 

 substance through the organic base of the ossicles with those 

 of the dorsal ligaments preceding and succeeding, it is probable 



Figs. 1-5. 



i 



3 



^=3 



Diagrams illustrating the origin of the muscular articulations of Crinoids. 



Fig. 1. The primitive joint face, with connective tissue binding ; the 

 two longitudinal ambulacral muscles are seen on the outer angles. 



Fig. 2. A joint face differentiated by the development of a transverse 

 ridge ; the connective tissue on either side has become ligamentous, and the 

 muscles have increased in size. 



Fig. 3. A joint face showing reduction of the internal fossa by pressure 

 of the " soft parts :" the ligament of the internal fossa is becoming denser ; 

 the muscles have increased in size. 



Fig. 4. The internal fossa has now become divided into two interarticu- 

 lar ligament fossae, lodging dense ligament bundles ; the muscles have 

 become still larger. 



Fig. 5. Radial face of one of the Zygometridse. 



that they act in sympathy with them, expanding and contract- 

 ing, in their small way as they do. It may be readily sup- 

 posed that the tension of the fibers in the syzygy is adjusted to 

 the ordinary movements of the crinoid arm. The dorsal liga- 

 ments are normally always antagonized more or less by the 

 powerful ventral musculature and ordinarily never contract to 

 their furthest capacity. If for any reason the ventral muscles 

 are rendered inert, as by the panic incident to capture, then 



