OSTEOLOGY 131 



and appeared to be strengthened by the occasional connec- 

 tion by ligament and bone with the hypocleidium. 



The most recent modification of this view is put forward 

 by PARKER, who has shown in Opisthocomus a needle-shaped 

 splint of bone lying upon the keel, and therefore independent 

 of it. 



The. development of the sternum throws a light upon the 

 homologies of its different parts in different birds, and in 

 other vertebrates. 



It is plain in the first place that the spina externa and 

 the spina interna have nothing whatever to do with the 

 manubrium sterni of the mammal ; for they are (in the bird) 

 secondary outgrowths, and not, as in the mammal, part of the 

 primitive sternum formed by concrescence of the ribs. The 

 same holds good of the posterior median region of the bone, 

 which is a secondary outgrowth, and can therefore have no 

 relations with the xiphoid process of the mammalian ster- 

 num ; what does correspond to the latter are the posterior 

 lateral processes of the avian sternum. 1 



Pelvis. 2 The pelvis consists of three pairs of bones, the 

 ilium, ischium, and pubis. In the young embryo these 

 bones form a continuous sheet of cartilage, but are all 

 separate distally ; the ilium is directed in an antero-posterior 



1 The literature of the sternum is large, and is to a considerable extent to be 

 found under the several groups. Memoirs of a wider scope are W. K. PARKER, 

 ' A Monograph on the Structure and Development of the Shoulder Girdle and 

 Sternum in the Vertebrata,' Ruy Soc. Publications, 1868 ; L'HERMINIEK, 

 ' Recherches sur la Marche d'Ossifications,' &c., M&m. Ac. Sci. 1830. The 

 history of the development of knowledge concerning the ossification of the 

 sternum and the classificatory results therefrom is treated by NEWTON in Diet. 

 Birds, ' Introduction.' Miss LINDSAY'S paper, already quoted, contains references 

 to the chief memoirs upon the subject. See also li. DIECK, DC Sterno Avium, 

 Diss. Inaug., Hal, 1867. 



'-' C. GEGENBAUR, ' Beitrage z. Kenntniss des Beckens der Vogel,' Jen. 

 Zi'itsclir. vi. p. 157 ; MEHNERT, ' Untersuchungen liber die Entwicklung des 

 Os pelvis d. Vogel,' Morph. J.B. xiii. 1888, p. 259 ; A. JOHNSON, ' On the 

 Development of the Pelvis Girdle, etc., in the Chick,' Quart. J. Micr. Sci. 1883, 

 p. 399 ; B. HAIJ, Jemfiii-ande Stxdicr ofvcr Foglarncs Backen, Lund, 1887, and 

 ' Morphologisk Byggnoden af Ilium,' &c., Act. Lund. Univ. xxii. 1887, p. 1 

 G. BAUR, ' Bemerkungen liber das Becken d. Vogel v. Dinosaurier,' Morph. J.B. 

 x. 1885, p. 613 ; A. BUNGE, Untersiichnngeti zur Entwicklungsgeschichtc des 

 Beckcngiirtcls, &c., Diss. Inaug., Dorpat, 1880. 



K 2 



