GREGORY: NOTHAncrUS, AN AMERICAN EOCENE PRIMATE 



111 



vertical and elongate and the ojiening for the ^^ertebral artery is large. Thus, the axis of the Old World 

 monkey is widely different from those of Notharctus and of Lemur, but is not so dissimilar to that of Cehus, 

 excei^t in minor characters. It differs widely from that of Mycetes (Alouatta), which is very massive, 

 with a wide neural spine and heavier transverse processes, in correlation with the more powerful neck 

 muscles. 



Cervicals 3 to 7. — The Notharctus and lemur ine neck vertebi-;p differ from those of carnivores in 

 being more depressed and extended anteroposteriorly with more delicate and shorter neural spines. The 

 transverse processes are more elongate anteroposteriorly, less twisted dorsoventrally and more appressed 

 laterally to the centra; the cervical vertebrse as a whole articulate in such a way that the head is held 

 more upward, while in carnivores it is more inclined downward. 



The third cervical \'ertebra is represented by a part of the neural arch and the zygapophysial facets 

 in No. 11478; it resembles that of Lemur in the anteroposterior elongation of the neural arches, but the 

 zygapophysial facets are somewhat more inclined dorsoventralty. 



As compared with the third cervical of Cehus, that of N'otharctus is stouter and more elongate; the 

 zygapophysial facets are less vertical; it differs from that of Macacus in the greater elongation of the 

 neiu'al arch and spine and in the smaller vertical diameter of the neural tunnel. 



The Fourth Cervical is represented by the neural arch in No. 11474 and is, on the whole, closest 

 to that of Lemur moncjoz. From that of Macacus it differs in having the anterior zygapophysial facet 

 much smaller and less extended vertically; the neural arch is also wider anteroposteriorly and the neural 

 tunnel smaller. 



The Fifth Cervical. — The centrum and neural arch are much as in Lemur fnongoz but the verte- 

 brarterial canal is smaller and the neural arch heavier than those of Cehus and Macacus. 



In the anteroposterior width of the neural arches Notharctus is much surpassed by Alouatta in which 

 the powerful cervical vertebrae broadly overlap each other and are provided with large neural spines 

 and broad transverse processes. A comparison wdth Cehus, however, suggests that these peculiarities 

 of Alouatta are not directl,y inherited from a lemmine type like Notharctus, but are merely a specializa- 

 tion of the cebid tyyio in adaptation to the great muscular development of the skull, neck, throat, and 

 thorax, all these in turn jxjssibly being a result of the enormous development of the vocal organs and lungs. 

 Cer^'icals 3, 4, and 5 of Alouatta differ from those of N^otJioretus in having the zygapophysial facets more 

 horizontal, the transverse processes much larger, and the posteroinferior prolongations of the centra 

 much more pronounced. 



Cervicals 6 and 7 are not preserved in Notharctus. In Lemur the sixth cervical differs from those 

 of Cehus and Macacus in having the inferior lamella of the transverse process much elongate anteropos- 

 teriorly. In the se\Tnth cervical of Lemur the diameter across the transverse processes is less than in 

 Cehus and much less than in Macacus. 



While regrettably incomplete, the fi-agmentary cervical vertebroe of Notharctus indicate that the 

 neck differed only in minor details from that of Lemur. As compared with those of Cehus and Macacus, 

 the individual vertebrae were probably narrower across the neural arches and transverse processes and 

 longer anteroposteriorly, and the neural and arterial openings were more restricted. 



Dorsals. — The first dorsal is known only from the centrum of No. 11474 which is nearest in form 

 to that of Lemur tnongoz; however, the anterior facet of the centrum is more nearly at light angles to 



