44 THE STKUCTUKE OF MAN 



From the above facts it is sufficiently evident that the 

 vertebral column was ancestrally furnished with a far greater 

 number of ribs than at present, and that the pleuro-peritoneal 

 cavity or coelom was once more capacious both at its cephalic 

 and caudal ends. Even at the present time, as already shown, 

 its modifications are not permanent. This is manifest, not only 

 from the reappearance of (so-called " supernumerary .") ribs, but 

 also from the decidedly rudimentary character of the eleventh and 

 twelfth ribs, which is rendered evident in several ways, more 

 especially in connection with variation in their size. The twelfth 

 rib, as might be expected, has a much wider range of variation 

 (2 to 27 cm.) than the eleventh (15 to 28 cm.); neither pair of 

 these reaches the sternum, and both show degeneration in their 

 detailed relationship to the vertebral column. These ribs have 

 no tubercle, and, consequently, no costo-transverse articulation ; 

 and the articulation of the head (capitulum) of each of them is 

 vertebral, instead of inter-vertebral, as in the case of those in 

 front of them. Occasionally a tendency to similar conditions 

 appears in the ninth and tenth pairs. Ontogeny shows that the 

 reduction of the eleventh and twelfth ribs is comparatively: 

 recent, since the rudiment of the costo-transverse articulation; 

 (tubercle) of the eleventh rib is still developed in the embryo. 



Turning now to the ensiform (or xiphoid) process of the 

 sternum, the variations in its shape, and more especially the 

 presence of occasional median fissures or foramina in it, show that 

 it arose from paired cartilages. It is, in fact, constricted off from 

 the eighth, and possibly also from the ninth pair of ribs. The 

 cartilages named, undoubtedly, at one time took part in the forma- 

 tion of the " sternal bands " to be described later, and thus the 

 number of ribs reaching the sternum may once have been greater 



as a strong process (Gegenbaur). These lower lateral spinous processes [anapophyses] 

 which are found only in Hylobates, among Anthropoids, arising from the bases of 

 the arches of the last two thoracic and sometimes from the first lumbar vertebrae, 

 according to Broca, occasionally occur in Negroes. It has been observed, further, 

 that the spinous processes of the cervical vertebra, which are, as a rule, forked in 

 Man, are simply pointed in the Hottentots ; and we here encounter a persistence of 

 the original simple condition which is normal among Anthropoids (R. Blanchard). 



Finally, it should be mentioned, that the groove on the dorsal side of the arch 

 of the human atlas for the reception of the vertebral artery is sometimes overarched 

 with bone, and converted into a foramen, such as is always found in most Primates, 

 Carnivora, and various other Mammals (Sappey). [And it is here worthy of remark 

 that the costo-transverse foramen, and its homologue the vertebarterial canal, may 

 in a similar way become completely surrounded by the transverse process 

 (Hippopotamus, Man?}. Cf. Jour. Anat. and Phys., vol. xxvii. p. 545.] 



