MAMMALS. 213 



more deteriorated in the adult (Plate XXV, figs. 16, 17, 19, p. cr. o. st.). In Sorex and 

 Crocidura the prge-coracoid has its own lenticular osseous centre within ; and in the old Amphi. 

 sorex fodicns (Plate XXVIII, fig. 8, p. cr.) this part is quite ossified. In Crocidura (Plate 

 XXVII, figs. 22, 23) the omosternum (o. st.) is an elegant claw-shaped ray of hyaline cartilage, 

 with an oval bony grain inside ; but in Sorex tetrayonurus this is nothing but a fibro-cartilage 

 (Plate XXVIII, figs. 1 and 5, o. st.)- I see no epicoracoid in either the Hedgehog or Chry- 

 sochlore ; but in Crocidura (Plate XXVII, figs. 22, 23, e. cr.) it exists on each side as an 

 elegant cordiform flap, partly hardened by endostosis. Supposing this piece and the omosternal 

 to be one, the relation of such a flap to the upper ridge in front of the pra>sternum would be 

 exactly what we see in the Mole (Plate XXVII, fig. 15, c. s. 4, p. st.) with regard to the distal 

 flap-shaped Meniscus. The epicoracoids of the Common Shrew (Sorex tetrayonurus) meet on the 

 anterior edge of the pra>sternum, and then coalesce (Plate XXVIII, figs. 1 and 5, e. cr.). 

 This is a repetition of what we have seen in the Lepidosiren, Coitus, &c., amongst the Fishes: 

 this is also to be seen in the Water-Shrew (fig. 8, e. cr.). 



The Sternum is very variable in the Insectivora ; it becomes segmented completely, though 

 without cavities, in the Shrews (Plate XXVII, fig. 22 ; and Plate XXVIII, fig. 1) ; the segmen- 

 tation becomes imperfect behind in the Mole (see Plate XXVII, figs. 7, 10, 15) ; and a section of 

 that of the adult shows that a nucleus had been left between the prse- and meso-stemum, which 

 becomes an epiphysis (fig. 7, ep.). In the Hedgehog (Plate XXV, fig. 16 and 19, old and 

 young) I find nothing more than feeble transverse notches below. The pra3-sternum is bilobate 

 in front in the Hedgehog, and trilobate in the Shrews ; in the Chrysochlore (Plate XXVII, 

 fig. 20, an ideal section, four diameters) it is a deep spoon, strongly keeled below. But the Mole 

 has the most extraordinary manubrium (" prse-sternum," see Plate XXVII, figs. 4, 5, 6, p. st., 

 old; and figs. 10 and 15, p. st., young) ; it is much larger than the whole of the meso-sternnm 

 (m. st.) in the young, where it is seen (fig. 10) to give off two pairs of wings; it is strongly 

 keeled below (figs. 5, 6, and 10), save at the front part, which is cordate; above (figs. 4 and 15) 

 it is rounded behind, scooped in the middle, and carinate in front. The hinder lateral projections 

 carry the first sternal ribs (figs. 10 and 15, s. r. 1) ; and between the manubrium and the first 

 meso-sternal we find the most perfect cleft. 



In the adult (Plate XXVII, fig. 6, st. f.) there is a fenestra, tending to separate the keel from 

 the body of the pra3-sternum. The ossification of the Sternum in the Insectivora is by ectoslosis, 

 seen in the youngest Talpa (Plate XXVII, fig. 10, pi. o. 1), where the bony matter is sur- 

 rounding the hinder third of the prag-sternum : in the next stage (fig. 15, pi. o. 2, m. t., o.) there 

 are three more azygous pleurosteal rings, and a " metosteon." The Shrews conform to this type ; 

 but in the Hedgehog (Plate XXV, figs. 16 and 19), which has the Sternum broad and flat behind, 

 as in the Ruminants, the meso-sternal bones are symmetrical. As a rule, the xiphoid part of 

 the sternum has a long ectosteal shaft, terminated by a rounded, flat lobe ; which, in old age, 

 becomes partly ossified by endostosis; this second "metosteon" is symmetrical in Sorex (Plate 

 XXVIII, fig. 1, x.), and in Crocidura (Plate XXVII, fig. 22, x.). These bony tracts are an exact 

 imitation of the primordial " xiphisternal horns." The xiphisternum of the Hedgehog (Plate 

 XXV, figs. 16, 19, x.) is emarginate by a "primordial notch," like the " prse-sternum." There is 

 no joint between the vertebral and sternal ribs in the Insectivora; the latter are always ossified 

 by endosfosis, yet they become very dense in the Mole. In ChrysocJtloris the " costa intermedia" 

 appears (Plate XXVII, fig. 21, i. r.), and is sometimes represented by two distinct ossicles. 



