GREGORY: NOTIIARCTUS, AN AMERICAN EOCENE PRIMATE 



lower lateral surfaee of the tail. Each segment passes l)ack\vard and ui)\var(l and is inserted into Ihe 

 transverse process of the next following \'ertebra. This series tends to depress the tail and to Hex each 

 segment on the one in front of it, and \\'itli the superior sacro-coccygeal series is ])owerfully developed 

 in all animals with prehensile tails. 



To sum up the general positions and functions of these muscles, we have (1) around Ihe neural spines 

 and metapoi^hysial processes of the lumbar, sacral, and caudal vertebne, the suiicrior interspinals (T) 

 (extensor cauda? medialis); (2) lateral to these the superior sacro-coccj^geal (R) series (extensor caudie 

 lateralis), lying between the zygapophyses and the transverse processes and serving to raise the tail; 

 (3) the intertransversal muscles (Z), (abductor cauda? internus), lying above and below the transverse 

 processes and on the sides of the centra, forming a ^\'edge-shaped series which move the tail from side to 

 side; (4) the iiiferii))- inlcrspiiiol (V) series on the ^'entl•al surface of the centra, attached to the chevrons 

 and serving to lower the tail; (5) the iscJtio-caudnh ((^) and the ilio-cnrci/f/cdis (U) rising from the inner 

 surface and dorsal rim of the ischium and ilium respectively, and being insei'ted into the transverse pi'o- 

 cesses and chevrons, especially of the coccygeal and upper caudal vertebra:^, pulling the tail powerfull}^ 

 downward and more or less laterally; (ti) the inferior sacro-coccygcal series rising from the transverse 

 processes and ridges of the caudals and inserted into the trans^'erse })rocesses of the second following xcv- 

 tebra, along with the intertransversals. 



The myological significance of the characters of the tail \Trtebra' of A'olhardii.s is therefore^ as fol- 

 lows. The slender coccygeal vertebra', with narrow transverse processes, and the smaller size of the facets 

 for the chevrons, all indicate more slender muscles at the root of the tail (especially the sujierior sacro- 

 coccygeal, ilio- and ischio-coccygeal and intertransversals). The subcylindrical form of the more posterior 

 caudals, their small transverse processes and small zygapophysial processes, in contrast with the depressed 

 vertebne and strong lateral and zygapophysial processes of Cehus, all indicate a non-prehensile tail with 

 weak intertransversals, superior and inferior sacro-coccygeals; it was probably almost whip-like as in 

 Propithecus, less muscular than in Lemur, and far less than in Cebus. 



Measurements of the Vertebra 





A'', oaborni 



A^. osborni 



tiji-annus 



L. mongoz 



L. mongoz 



L. varim 





No. 11474 



No. 11473 



No. 11478 



No. 22886 



No. 312.54 



No. 35396 





mm. 



mm. 



mm. 



mm. 



mm. 



mm. 



Total Length of Liniil)ar WTtehni' (L2-L7) 



',)2 . 





93 . est.- 





91. 3 



119. est. 



Atlas, anteropost diain., above verte- 















l>rarterial foramen 











G.o 





Cervical 3, anterior zygapophysis to pos- 















terior zygapophysis 











5 . 5 



s. 



Cervical 4, prezygapophysis to postzyg. 















facet, ant. post, diameter 



(). 









•5 . 5 



8. 



Dorsal 1, ant. posterior diani. of eentrum 











6. 



7 . 5 



" 1, transverse " " 



7 . 4 est. 









9. 





" 2, ant. post. " " " 



S. 









5 . 9 



7.(j 



" 2, transverse " " " 



8. 









8.3 



10.2 



" 3, ant. post. " " " 



7.8 









(j.8 



8.7 



" 3, extreme trans. " " " 



8.. 5 









7.4 



](). 



" 4, ant. post. " " " 



8.3 









. G. 



10. est. 



" 4, transverse " " " 











S. 





" 5, ant. post. " " " 



7.3 









7 . 



g..') est. 



