102 



A srhall CLAVICULAR JOINT inserted between the two hands proceeding 

 from one scapula, separates the integument and vessels under it in their pro- 

 gress upwards. (PL. n. fig. 5.) 



CAPITAL PLATES. (PL. iv. fig. 30. to 39.)~-The plates forming the upper 

 part of the integument over the abdominal eavity, I have named capital plates; 

 they have like the pectoral plates different angles, but are covered by a thicker 

 muscle, which is connected (although only slightly so, as appears from the 

 pectoral plates not exhibiting those folds which result from strong muscular 

 action) with those proceeding from the pelvis over the first costals, and laterally 

 extending upwards over the intercostals and pectorals. It receives a new 

 impulse from a sphincter-like muscle placed in the centre, which is capable 

 of forcing up the margin of the mouth into an elongated and protruding 

 proboscis, and at the same time contracting the area between the arms, 

 and thereby enabled to pull these up, and bring the hands and fingers 

 together in a close fasciculus. Meanwhile the muscle or portion of muscle 

 covering each capital plate, is also able by its contraction to draw up 

 in the centre, and thereby to form a more or less elongated tubercle, whose office 

 it probably is to push on the food to the mouth, so that the whole integument 

 thus assumes an echinated appearance. When the contractile force is most 

 strongly exhibited, the proboscis also becomes studded with similar tubercles 

 (PL. n. fig. 1 . and 2.) but otherwise those tubercles are exhibited only on the 

 capital plates more remote from the centre, those near the proboscis remain- 

 ing smooth. (PL n. fig. 6. and 7.) On the relaxation of the muscles these 

 tubercles disappear the proboscis gradually subsides the space between the 

 arms widen and the fingers are permitted to expand. Specimens in every 

 state of contraction occur in a fossil state, and most distinctly prove that the 

 markings and appearances described, can be ascribed only to muscular action. 



