(iKK(;()KY: xo'riiAh'cn s, an American eocene primate 



The centra are inoi'e compressed l)el()\v and are excavated anteroposteriurly, whereas in Ccbus tliey are 

 flatter on the lower surface, and still more so in Macacus. The transverse processes are far less 

 extended laterally, also the column narrows very rapidly from the lumbars to the mid-dorsal region, 

 whereas in Macacus, and to a less extent in Cebus, it narrows very gradually as we pass forward. 



Alouatta, in correlation with the great size and nmscular development of the thorax, has the dorsal 

 centra and neural spines veiy heavy, the latter closely imbricating; the facets for the tubercles of the 

 ribs are very wide; the anterior dorsal centra are somewhat compressed below. In all these features 

 Alouatta appears to be a specialized cebid rather than a primitive derivative of the lemurs. 



In the marmosets the dorsal centra appear to be relatively shorter and wider than those of Notharcius 

 and Lemur, the regional differentiation of the neural spines is sharper; l)ut everywhere there is a fvuula- 

 mental resemblance with the dorsals of A^otharctus. 



Musculature of the Cervical and Dorsal Regions. — The agreement in form of the cervical, 

 dorsal, lumbar and sacral vertebra of Notharctas with those of lemurs, taken in conjunction with the 

 similar agreement in the limb bones, is so close that we may confidently infer that the modern lennu- 

 (Fig. 2) has preserved the inusculature of the Eocene lemur with very little change. 



The neck of Lemur is much longer than that of either the South American monkeys or the catarrhines. 

 In general, the neck muscles are arranged in such a way that the head is held niorc^ forwai'd and not so 

 much at right angles to the column as it is in the higher primates, as is indicated also l)y the iact that in 

 the latter the neck vertebrae are compressed anteroposteriorly and widened transversely. 



The thorax is less expanded than that- of higher primates, the ribs being shorter and less robust; 

 consequently the dorsal vertebrae are also less robust and have less widely extended transverse processes. 



The eighth dorsal is the anticlinal, at which point the dorsal muscles end and the luml^ar muscles 

 become predominant. 



Lumbars. — In contrast with those of carnivores, the lumbars of Ah)(h(rrclus and of Lemur differ 

 in the form of the transverse processes; these are short and anteroposteriorly bi'oad, whereas in tyi)ical 

 carnivores they are long, narrow and sharply turned forward, a condition which is perhaps correlated 

 with the superior cursorial powers of the hind limbs of carnivores. The centra of the carnivore lumbars 

 are also flatter interiorly than are those of lemurs. 



Of the lumbar vertebrae of Notharcius the first and eighth are absent in Nos. 11474 and 11478, but 

 lumbars 2-7 are represented in both specimens by more or less complete vertebrae. The lumbar centra 

 are lemur-like: shallow vertically (Fig. 27), elongate anteroposteriorly (Plate XXXIII), with more or 

 less sharp median inferior keels; whereas in Macacus they are deeper vertically and much wider interi- 

 orly, with median keels reduced or absent. Cebus is to some extent intermediate, but the centra are 

 deeper vertically and wider transversely than they are in lemurs. 



The neural spines of Notharcius are stout and forwardly directed as in Lemur, although somewhat 

 heavier than in L. mougoz; in Macacus ihe neural spines are nuich lengthened anteroposteriorly with 

 depressed tips. In Cebus they are intermediate in form between those of Notharctus and of Macacus. 

 The bases of the neural spines exhibit no traces of the paired " hyperapophyses " (Mivart ) on either 

 side of the mid-line which are characteristic of Cebus and Aloualla. 



As in other ]:)rimates, the lumbars of Notharctus bear posteriorly directed processes (anapophyses) 

 immediately external to and beneath the postzygapophyses. The transverse processes, so far as pre- 

 served, are similar to those of Lemur hni somewhat wider at the base; they spring from the sides of the 



