GREGORY 



NO'l'lIAh'CTlf.S, AN AMERICAN EOCENl!] PRIMATE 



115 



ated with the habit of sitting ui)i'ifi;iit and with the presence of expanded iscliial tul)erosities. In man 

 these features of the lumbar centra are accentuated. Cebus, in the form of its lumbar centra, is perhaps 

 nearer to Macacus than to the lemurs. Hapale, on the other hand, is somewhat nearer to the lemurs. 

 Likewise the long forwardly directed neural spines of the lumbars in Nolhardus and Lemur are associated 

 with a more horizontal pose, whereas the widened and erect neural spines of the lumbars of Macacus 

 are associated with a more upright j^ose in sitting. This hne of specialization of the lumbar spines is 

 carried gradually through the Old World monkeys and great apes and culminates in man, in which the 

 lumbar spines are either vertical or directed backward. From these vertical or backw'ardly directed 

 lumbar spines in man slips of the erector spinte muscle pass forward, or upward, toward the dorsal vertebra^, 

 and assist in extending the backbone, i. e., in throwing the lumbar region into a ventrally convex curve; 

 they therefore render important service in the act of sitting upright as well as in bipedal locomotion. 

 In the more C{uadrupedal lemui's, on the other hand, these nmscular slips, passing from the forwardly 

 directed lumbar spines, are especially useful in the act of leaping, by raising the fore part of the body. 



The \'aried form and position of the trans\'erse processes of the lumbar vertebree in lemurs and higher 

 primates are likewise associated with differences in methods of locomotion and conseciuently in the form 

 and proportions of certain muscles, especially the quadratus lumborum and psoas. In man the quad- 

 ratus lumborum arises in part from the crest of the ilium and from the transverse processes of the lumbar 

 vertebrse (except the first and second?) and is inserted into the last rib and the transverse processes of 

 lumbars 1,2; the transverse processes of the human lumbars are directed dorsally so that the quadratus 

 laml)orum assists in extending the column and thus in maintaining the upright jiose. In lemurs, on 

 the other hand, th(> trans\e]'se jirocesses of the lumbars arc directed do\\nward and forward and the 

 quadratus lumljorum doubtless assists in flexing the column, in the act of leaping. The psoas in man 

 arises from the ventroexternal region of the posterior dorsal and lumbar vertel)rn', especially from the 

 transverse processes; it passes caudad in front of the pelvis and is inserted on the lesser trochanter, on 

 the inner side of the fenuu'; it cotiperates with the iliacus and other muscles in flexing or pulling forward 

 the femur, and in preventing the body from falling ()\'er backward. In the quadrupedal primates it is 

 especially powerful in drawing the femur forward, and is attached to the posterior branch of the trans- 

 verse processes. 



In short, the lemurs, including N'dlharciu.s, in correlation with their su]oerior leaping powers and 

 more horizontal pose in sitting, have the stout lumbar neural spines directed forward, apparently in cor- 

 relation with the forward pull of the erector spina? ; they have the lumbar transverse processes broad and 

 forwardly directed, this implying powerful quadratus lumborum muscles, used in flexing the lumbar 

 region in leaping; and finally, the transverse i^rocesses are provided with posterior l^ranches for the 

 insertion of the powerful jisoas nuiscles, used in drawing the femora forward. 



Differences in the form and aiTangement of the nuiscles of the dorsal and lumbar regions no doul)t 

 determine in part not only the characteristic differences between dorsal and lunil)ar \ ertebra', but also 

 the more or less transitional character of the posterior "dorsals" and anterior "lumbars"; for in this 

 region the muscles of the ribs and diaphragm, as well as the longissimus dorsi and the spinalis dorsi, 

 give place to the (luadratus luml)orum, the i-)Soas and the erector spinas 



Sacrum. - The sacrum is partially preserved in Nos. 11474 and 11478. The closest resemblances 

 are with Levmr, but the second and third sacrals are smaller, in correlation with the more slender tail. 

 As in Lemur, the articular surface for the ilium is borne almost entirely by the first sacral vertebra (Plate 



