50 COMPARATIVE ANATOMY. 



or four ribs reach to the sternum, 1 and are not always completely 

 segmented off from it. 



The ribs of Birds exhibit a much more marked segmentation 

 into vertebral a'id sternal portions, and this evidently stands in 

 relation to respiration; they moreover develop so-called unei- 

 nate processes Kiv; Mli. i'n . In t his latter, as in many other 

 ]ioints they show n relation to eeriain Reptiles \ i;:. 1 i a t t ma ami 

 Crocodiles). 



Tin' ill'- of Areha'opteryx are of special interest, as they are more simi- 

 lar to those of lleptih-s than to those of Birds, though they do not closely 

 res,.]nhh' tin' former. Thc-ir structure is delicate, their ends aiv pointed. 

 and no nneinate processes liavi- been ob-,-1 ved : in transverse section they arc 

 ellip-oidal, and m>t llattened like those of Birds. Whether a eonneetion with 

 a brra-t-bone existed is not certainly proved, as nothing is known of a st< mum 

 or of Menial ribs. The breast-bone must at any rate have been very small, as 

 the ' abdominal ribs" extend far forwards; it was probably provided with a 

 keel, for the quills of the wing are well developed. 



FIG. 37. COSTAL AKCII OF MAN. 



U'A', centrum of vertebra ; Ft, transverse process ; Ps, neural spine ; Cp. body of 

 rib; Ca, capitulum ; Co, neck; Tb, tuberculum ; Kn, cartilaginous (sternal) 

 rib ; St, sternum. 



It has already been mentioned that the cervical ribs and transverse 

 processes may become united together in representatives of all the Amniota, 

 and the fusion between the ribs and dermal plates in Chelonians may In- 

 here noted. 



In the true ribs of Mammals, and especially in those of Man. 

 a capitulum, a neck, a tuberculum, and a body may be distinguished 



(Fig. 37). The capitulum articulates with the centrum, and tin- 

 tuberculum with the transverse process of the vertebra. The 

 number of ribs which reach the sternum varies considerably. 



1 In Crocodiles, ei;,'ht to nine ribs react tlie 1'ivast -luine ; iii 1'iivils, 



i L'M. An osMiiention nf the inscriptionee temlineje ni' the reetus abdominis takes 

 jdafie in Crocodile.-, ami II at t eri.t. and similar struotureB (so-called "alid"inin;il 

 nlis '') (ir.'ur in numerous fns-il llcjitiles ( Nut Imsaiirns of the Trias, |-'.iialio> ; uii us nf 

 the Jurassj. . I'll rudaetyiiis. &C.). ArchftOpteiyX alsn pOSSCSSed t \\elve t" third in 

 well-developnl " al n 1< MM inal ril 's. " The.se must iM't ! r, , lit, unided with the remains 

 of true abdominal ribs, \vhieh persist without the convspoinliii;,' vertebral portion 

 in the Chameleiiii niid ivrtnin Birds (W. K. 1'arki-rV 



