Elements of Comparative Anatomy (1878) Elements of Comparative Anatomy elementsofcompar78gege Year: 1878 APPEXDICULAE SKELETON OF VERTEBRATA. 473 whicli it occupies, it is known as tlie tlioracic (slioulder), or pelvic (hip) girdle. Tlie skeleton of tlie free appendage is attached to the extremity of the girdle. When simplest, this is made up of cartilaginous rods (rays), which differ in their size, segmentation, and relation to one another. One of these rays is larger than the rest, and has a number of other rays attached to its sides. I have given the name of Archipterygium to the ground-fo
Elements of Comparative Anatomy (1878) Elements of Comparative Anatomy elementsofcompar78gege Year: 1878 APPEXDICULAE SKELETON OF VERTEBRATA. 473 whicli it occupies, it is known as tlie tlioracic (slioulder), or pelvic (hip) girdle. Tlie skeleton of tlie free appendage is attached to the extremity of the girdle. When simplest, this is made up of cartilaginous rods (rays), which differ in their size, segmentation, and relation to one another. One of these rays is larger than the rest, and has a number of other rays attached to its sides. I have given the name of Archipterygium to the ground-form of the skeleton, which extends from the limb-bearing girdle into the free appendage. The primary ray is the stem of this ai'chipterygium, the characters of which enable us to follow out the lines of development of the skeleton of the appendage. Cartilaginous arches beset with rays form the branchial skeleton. The form of skeleton of the appen- dages may be compared Avith them; and we are led to the conclusion that it is possible that they may have been derived from such forms. In the branchial skeleton of the Selachii the cartilaginous bars are beset with simple rays (Fig. 260, a h). In many, a median one is a Fig. 260. Diagrams to illustrate the homodynamy of the appeudicular skeleton with that of the branchiee. ah cd Branchial arches of Selachii. e Archipterygium. developed to a greater size. As the surrounding rays become smaller, and approach the larger one (c), we get an intermediate step towards that arrangement in which the larger median ray carries a few smaller ones (d). This differentiation of one ray, which is thereby raised to a higher grade, may be connected with the primi- tive form of the appendicular skeleton; and, as we compare the girdle with a branchial arch, so we may compare the median ray and its secondary investment of rays with the skeleton of the free appendage. We meet with greater difficulties when we come to examine the topographical relations
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