74 THE STRUCTURE OF MAN 



shoulder girdle is loosely attached to its ribs by muscles, the 

 pelvic by firm ligaments and a definite articulation. 1 



In the human embryo, as in all living Eeptiles, Birds, and 

 Mammals, the embryonic pelvis is triradiate, its cellular blastema 

 at first forming one mass with that of the developing femur : this 

 condition I have traced through the whole series of Vertebrates. 2 

 After the pelvic blastema has, at a later stage, become differ- 

 entiated from that of the femur, which is the first to become 

 cartilaginous, the ilium, ischium, and pubis are laid down as 

 distinct chondrifications. The fusion of the acetabular portion 

 of these three pelvic cartilages takes place in the following 

 order : first, the ischium alone unites with the ilium, and later, 

 the ilium with the pubis. The ischium and the pubis do not 

 send out acetabular processes towards one another, and for this 

 reason a space is left at their point of apposition. 



[The bone to which in the adult human subject the term 

 pubis was first applied, is formed by the union of two distinct ele- 

 ments a main one arising in utero, and a lesser, arising during 

 the thirteenth year 3 within the acetabular region, and completely 

 excluding its neighbour from that cavity. The latter element 

 is of regular occurrence among the lower Mammalia, and being 

 in them of considerable proportions has received the name 

 " cotyloid bone " or " os acetabuli." In accordance, however, with 

 its ultimate fate, it may be more appropriately termed the 

 dorso-pubic element, and its neighbour the ventro-pubic. 4 Thus 

 considered, comparison of the pubis with the coracoid (ante, 

 p. 72) shows that in Mammals, and in them alone among living 

 Vertebrates, each consists of two elements, of which one 

 (epicoracoid and pre - pubic element) is excluded from the 

 articular facet (glenoid cavity and acetabulum).] 



In no other Mammals do the iliac bones diverge so greatly 



1 This difference appears less marked, and may altogether vanish, when we 

 compare the [lower vertebrata. Among Chelonians the shoulder girdle very generally 

 articulates upon the anterior thoracic vertebrae ; and in] Fishes a firm connection 

 is established between the shoulder girdle and the skull (Osteichthyes), or even 

 between the former and the vertebral column (Rays), [such as is seen also in many 

 Frogs and Toads, and may, under rare conditions, occur in Man himself.] In 

 certain Salamanders we find, on the rib approximate to the inner border of the 

 suprascapular, a plate-like cartilaginous expansion, which is fastened to the shoulder 

 girdle by means of ligaments ; [this, however, has probably to do with protection of 

 an adjacent pulsatile "lymph-heart."] 



a The author here refers in the original German to his " Gliedmassen Skelet der 

 WirbeWiicrc," Jena, 1892. 



3 [Cf. Krause, Month. Internat. Jour. Anat. and Hist., vol. ii. p. 150.] 



4 [Cf. Howes, Jour. Anat. and Phys., vol. xxvii. p. 550.] 



