3 



Leddene paa den nederste Trediedel af Stilken ere 

 væsentlig forskjellige fra de øvrige. De ere tykkere, gro- 

 vere bygget, 3""" lange, 2""" brede i Enderne og paa Midten 

 1""", Tab.. I, Fig. la. 2 e. 3 e, 6. De ere fuldstændigt 

 elliptiske og meget udvidede i begge Ender, medens de ere 

 næsten runde og indknebne paa Midten, Tab. I, Fig. 3 e, 

 hvilket ovennævnte Maal ogsaa udviser. Men foruden dette 

 er der ogsaa det mærkelige ved disse Led, at Retningen 

 af den øverste Leddeflade er ganske modsat den nederste, 

 saaledes at de krydse hinanden under rette Vinkler, Tab. 

 I, Fig. 3 f. 



Leddeforbindelsen paa denne Del af Stilken bliver 

 derfor særegen, idet hvert andet Leds (Ellipsens) største 

 Axe følger Stilkens Længdeaxe, imedens hvert andet følger 

 Tveraxen, Tab. I, Fig. 3 g. Stilken faar derved et vredent 

 Ldseende. Paa unge Exemplarer ser det ud, som hvert 

 saadant Led har været delt i to Stykker, Tab. I. Fig. 2 f, 

 hvoraf den ene, ovre Ende — den egentlige Leddeflade — 

 er elliptisk, Tab. I, Fig. 2 g, den anden, nedre, næsten 

 rund; de to runde Ender danne i Begyndelsen en syzygial 

 Forbindelse, men senere voxe de saa nøie sammen, .at de 

 ofte ikke engang efterlade Spor af den tidligere adskilte 

 Tilstand, Tab. I. Fig. 3 h. 



Ligesom Leddene i deres ydre Form ere saa høist 

 forskjellige fra de høiere oppe paa Stilken værende Led, 

 saaledes ere de ogsaa forskjellige i deres indre Bygning. 

 Leddefladen er fuldstændig elliptisk, Tab. I, Fig. 6, og fra 

 dens indre Væg udgaar paa hver Side fra diametralt mod- 

 satte Punkter en Kalkkam, Tab. I, Fig. 6 a, der er pyra- 

 midedannet, med sin bredere Del eller Basis fastvoxet 

 til Væggen, og den tilspidsede, fri Del ragende frem i 

 Leddets Hulhed til henimod dennes Midte, Tab. I, Fig. 6 b, 

 hvorved der imellem begge Spidser kun bliver et smalt 

 Rum, som udfyldes af Centralstrængen, der her lober i 

 en stærk, membranøs Skede og ikke i en Kalkkanal, som 

 Tilfældet er høiere oppe paa Stilken. 



Paa den øverste Leddeflade har denne fremragende 

 Kalkkam paa Midten en langsgaaende. ophoiet Kalkliste, 

 Tab. I, Fig. 6 c, der er forsynet med en Række Tænder 

 paa hver Side, og paa den underste Leddeflade tindes paa 

 Kalkkammen en paalangsgaaende Fure med Sideindsnit, 

 som optager Listen og Tænderne paa den tilsvarende, under- 

 liggende Leddeflade saaledes, at hvert Led paa denne 

 Maade faar en meget fast Forbindelse. Paa Siderne af 

 Kalkkammen er Leddehulhederne, Tab. I, Fig. 6 d. udfyldte 

 af stærke, tendinøse Strænge. Hvor Leddefladen har sin 

 længste Axe, danner Kalkkammen med sin brede Basis en 

 liden Fremstaaenhed. der paa Leddets ydre Flade, lige 

 ved Ledderanden, danner en liden Knop. 



Det nederste Led paa Stilken, det egentlige Rodled, 

 er meget kort. omtrent lige tykt som langt, og har stundom 

 en trekantet Form, Tal). I, Fig. 3 i. Dets underste Ende 

 er afdelt i 2, sjeldnere 3, næsten runde, lidt fordyberle 



The joints on the lowest third part of the stalk are 

 materially different from the others. They are thicker, 

 coarser in structure, 3 mm in length, 2""" in breadth at the 

 extremities and 1""" in the middle (Pl. I, figs. la, 2 e. 

 3 e, 6). They are perfectly elliptical and greatly expanded 

 at both extremities, while they are almost round and con- 

 stricted in the middle (Pl. I, fig. 3 e). which the above 

 given measurements also shows. But, besides that, there is 

 also in these joints the remarkable feature, that the direc- 

 tion of the uppermost articular surface is directly the op- 

 posite of the lowest one, so that they cross each other at 

 right angles (Pl. I, fig. 3 f). 



The articular connection on this part of the stalk is 

 therefore peeuliar, in as much that the greatest axis of 

 every second joint (the ellipse) follows the longitudinal axis 

 of the stalk. whilst each of the others follows the trans- 

 versal axis (Pl. I, fig. 3 g). The stalk thus acquires a 

 twisted appearance. In young specimens it appears as if 

 each such joint had been divided into two pieces (Pl. I. 

 fig. 2 f), of which the one, superior extremity — the real 

 articular surface — is elliptical (Pl. I, fig. 2 g), the other. 

 the inferior, almost round; the two round extremities form 

 at the commeueement a syzygial connection, but subsequently 

 grow so intimately together that they frequently do no1 

 even leave a trace of the earlier separate condition (Pl. I. 

 fig. 3 li). 



Just as the joints are so highly different in their 

 external form from the joints higher up the stalk, so are 

 they also different in their inner structure. The articular 

 surface is perfectly elliptical (Pl. I, fig. 6), and their issues 

 from its inner wall on each side, from diametrically op- 

 posite points. a calcareous ridge (Pl. I, fig. 6 a), formed 

 pyramidically, with its broader part or base firmly concreted 

 to the wall and the acuminate free portion projecting into 

 the cavity of the joint to nearly its middle (Pl. I, fig. 6 b), 

 so that between both points there only remains a narrow 

 space that is occupied by the central cord, which here 

 runs in a strong membranous sheath and not in a cal- 

 careous canal as is the case higher up the stalk. 



On the uppermost articular surface this projecting 

 calcareous ridge has a longitudinal, elevated calcareous 

 fillet in the middle (Pl. I, fig. 6 c), which is fumished 

 with a series of teeth on each side; and on the lowest 

 articular surface there is found, on the calcareous ridge. 

 a longitudinal groove with lateral incision which takes in 

 the fillet and the teeth of the corresponding subjacent ar- 

 ticular surface, in such a manner that each joint obtains 

 a Very firm connection. On the sides of the calcareous 

 ridge are the articular cavities (Pl. I. fig. 6 d), occupied 

 by strong, tendinous cords. Where the articular surface 

 has its greatest axis, the calcareous ridge with its broad 

 base forms a small projection which, on the outer surface 

 of the joint, just at the articular margin, forms a little bud. 



The lowest joint on the stalk — the real root-joint — 

 is very short, about as thick as it is long, and occasionallv 

 has a triangular shape (Pl. I. fig. 3 i). Its lowest extremity 

 is divided into 2, more rarely 3, almost round, slightly 



