FLEXIBLE BONDS OF UNION AND SUPPORT. 51 



matrix and cells are abundant, the fibres terminating 

 in a network after repeated branching. The ligament 

 probably serves to drag the rib forward after the contraction 

 of the intercostal muscles has pulled it backwards. Tho 

 ligament has been left attached to the vertebra? from which 

 the ribs have been removed. (Fig. 4.) 



LIMBS. 



B. 23. Right pectoral fin of a Monk-fish (Rhina sgnatina), show- 

 ing a series of elastic ligaments situated upon the ventral 

 surface of the fin. The largest and most important of these 

 ligaments (indicated by a black bristle) connects the 

 shoulder-girdle with the two anterior basal pterygia ; it lies 

 outside the joint capsule. The remainder of the series are 

 related in a similar manner to the basio-radial and proximal 

 row of interradial joints. On their inner side they are in close 

 connexion with the interarticular fibrous mass and covered 

 on the outside by the perichondrium. No such ligaments 

 are present on the dorsum of the fin. A similar condition 

 was found in Acanthias, but not in Myllobatis or the Skate. 



B. 24. A longitudinal section through the mesopterygium, a 

 radius, and part of the shoulder-girdle of a Monk-fish 

 (Rhina squatina), showing the elastic ligament that con- 

 nects the shoulder-girdle with the ventral surface of the 

 pterygium and its relations to the joint capsule. The 

 capsule has been removed from the dorsal surface of the 

 joint, 



JOINTS. 



Without known function, mostly the result of periodicity in rate 

 or nature of growth. 



PLANTS. 



B. 25. Terminal branch of a Euphorbia (E. neriifoUa) stained by 

 cupric acetate. The stem is jointed, showing a series of 

 constrictions. The joints do not increase the flexibility of 

 the stem, nor serve as places of ready fracture as in Cacti. 

 They probably only indicate periodicity in growth, and 

 have no function. The terminal segments bear large leaves. 



Royal Gardens, Kew. 

 E2 



