THE SKELETON 43 
dition, however, the internal and external intercostal muscles 
between this cervical and the first thoracic rib are well developed 
in cases like that above figured; indeed this is so even when 
(as occasionally happens) the fibrous connecting band is wanting 
(Leboucq). The sternal portion of the rib is as a rule very 
weakly developed, sometimes free, sometimes partly fused with 
the first thoracic rib. The vertebral end varies much in form, 
size, and articulation upon the vertebral column; and further, its 
relations to the first thoracic rib may, as Leboucq has shown, vary 
greatly. It may either be altogether fused with the latter, merely 
loosely attached to it by connective tissue, or actually articulated 
with it. In the first case, the first thoracic rib appears forked 
at its vertebral end, and this (according to P. J. van Beneden) 
is the rule in many Cetaceans. 
Apart, however, from such cases as these, a further proof of 
the former existence of cervical ribs in Mammals is derived from 
the study of the adult Edentata. Among these, Cholwpus has 
normally only six cervical vertebre [defined as those destitute of 
free ribs]." Bradypus infuscatus and B. tridactylus illustrate 
the other extreme, possessing normally nine such vertebra ; 
while &. cuculliger has either eight or nine. In the latter 
cases the upper end of the thorax has undergone greater reduction 
than in any other Mammal. 
The fact that in Man the first thoracic rib is probably 
beginning to degenerate,” and is at the present time in process 
of atrophy, is established by the not infrequent recurrence of 
undoubted cases of its abortive development. Such have been 
recorded by Struthers, Grosse, Hunauld, Gruber, Turner, Leboucq, 
and others (cf Fig. 27, B). The description given above of 
the seventh cervical rib might, in these cases, be apphed to the first 
thoracic. Nevertheless, I believe, for reasons to be given later, 
that should reduction at the upper end of the thorax advance, 
it will do so far more slowly than at the lower, or indeed that 
it may even be arrested for an indefinite period (cf. p. 45). 
1 A similar numerical reduction of the cervical vertebre occurs also in the 
Manatee [but there is reason for believing that it is in that animal due to the 
excalation of at least the body of one of these, and not to the assumption of thoracic 
characters by the last of the series. ] 
* I should like here to raise the question whether this tendency to reduction at 
the upper end of the thorax may not be a determining factor in the degeneration so 
frequently found to be commencing at the top of the lungs ? (cf. infra). 
* It is interesting here to note that ventrally to the transverse process of the sixth 
cervical vertebra, there often arises, on either side, a projection, which might be 
claimed as a vestigial structure, since in most Mammals it stands out prominently 
