. Elements of the comparative anatomy of vertebrates. Anatomy, Comparative; Vertebrates -- Anatomy. 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 inter
. Elements of the comparative anatomy of vertebrates. Anatomy, Comparative; Vertebrates -- Anatomy. 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-,-1ved : 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 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 Cr
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