30 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 82 



dividing line is a transverse inflection, or " suture," passing through 

 the bases of the sternal apophyses (fig. 18 C, k). The inflection is 

 usually strongly sclerotized, forming an internal ridge evidently de- 

 signed to brace the sternum and to support the apophyses (figs. 21 B, 

 31, k) ; it sometimes remains weak, however, and establishes a line 

 of flexibility in the sternum. In either case the sternum is demarked 

 by the furcal ridge and its suture (/e) into a pref ureal area (fig. 18 C, 

 Bs) and into a post f ureal area (SI). 



The anterior region of the sternum has been variously named 

 sternum, in a restricted sense, antcsternum, mcsosternum, basistermim, 

 eusternum, and sternannuin; the second has been called sternellmn, 

 poststernum, metasternum, and fureasternum. There are objections 

 to all but one of these terms. "Antesternum " and " poststernum " 

 (Amans, 1885) are applicable in some cases, but there is often a pre- 

 sternal piece before the " antesternum," and very commonly the inter- 

 segmental spina-bearing plate forms an actual postemal element of the 

 definitive sternum behind the " poststernum." " Mesosternum " and 

 " metasternum " (Berlese, 1909) violate the priority of the segm.ental 

 prefixes. " Basisternum " and " fureasternum " (Crampton, 1909) are 

 misleading because the part designated by the first is not basal, and that 

 bearing the second name does not always carry the furcal apophyses. 

 " Eusternum " (Snodgrass, 1910) implies that the part so named is 

 the " true " sternum, which it is not. " Sternannum " (Mac Gillivray, 

 1923) has no grammatical standing, so far as the writer can find. 

 " Sternellum " (MacLeay, 1830) alone can be given a clean bill. Of 

 the terms applied to the prefurcal area, however, " basisternum " ap- 

 pears to be the least objectionable. In the present paper, therefore, 

 the writer adopts the following terms for the principal divisions of the 

 definitive sternum (fig. 18 D) : presternum (Ps), basisternum (Bs), 

 sternellum (SI), and spinasternum {Ss). The first three are secon- 

 dary subdivisions of the primary segmental sternum ; the fourth is the 

 intersegmental intersternite. To the primary sternal region there may 

 be added on each side a subcoxal laterosternite (Ls). 



The parts of the definitive thoracic sternum as described here fit 

 exactly with the definitions of the sternal sclerites given by Weber 

 (1928, pp. 250, 251), with the understanding that the term " sternel- 

 lum " is substituted for " fureasternum," and that the poststernite is 

 the intersegmental spinasternite. This idea of the sternal composition 

 differs from Crampton's (1909) conception in that the fundamental 

 transverse dividing line of the sternum is assumed to be the furcal 

 suture (k) between the bases of the sternal apophyses, and not a divi- 



