MR. W. H. PLOWEK ON THE OSTEOLOGY OF THE SPERM-WHALE. 355 



latter, in like manner, appears to be the result of fusion across the middle line of two 

 lateral portions ; so that the stenmm was originally ossified from three pairs of distinct 

 centres, as shown by Wall in the figure of the young skeleton at Sydney. 



The contiguous borders of the large anterior pieces do not come in contact for the 

 whole of their length, but leave an oval median aperture, 11" long, and 8" in greatest 

 width, the fore end of which is 7" from the anterior margin of the bone. The greatest 

 breadth across the entire sternum, close to its anterior end, is 42^" in a straight line. 

 Its extreme length is 47". The posterior piece, of an irregularly quadilateral form, is 

 lOf " wide near the front, and contracts to 6J", expanding again slightly at the hinder 

 extremity. Its extreme length is 14f", being more produced backwards on the left 

 side than on the right. As seen in the side view (PI. LX. fig. 4), the whole bone is con- 

 siderably curved in the longitudinal dii-ection, and is very unequal in thickness. The 

 superior lateral angles form very large and massive prominences, bearing rugged oval 

 surfaces for articulation -with the expanded lower end of the first rib. Below this the 

 bone becomes comparatively slender, and then thickens again at the junction of the first 

 and second piece, where is situated a small cup-shaped articular sm'face for the cartilage 

 of the second rib. The second piece retains throughout a considerable vertical thickness. 

 At its hinder extremity is the surface for the attachment of the cartilages of the third 

 rib. 



The sternum of the Caithness Cachalot presents the same general form, but is broader 

 in proportion to its length. The two anterior pieces are united together for a space of 

 8" in front of the median foramen, but are still disjoined behind it. The foramen is 

 smaller and more circular, being 6" in length by 5" in breadth. The most notable dif- 

 ference, however, is in the hinder piece, which is represented only by a median spheroidal 

 nodule of bone, 4" in diameter, which fortunately still remains in situ, imbedded in a 

 mass of dried cartilage. The greatest breadth of this sternum is 46", its length 32". 



The sternum of the Yorkshire skeleton comes nearer again to the Tasmanian, both 

 in general proportions and in the development of the hinder portion. Its extreme 

 breadth is 44", and its length, including the hinder piece, which is 12", is 45". As in 

 the last-described adult specimen, the anterior portions are united across the median 

 line in front of the foramen, but not behind. The foramen itself is of a different form 

 from that in either of the others, being very long and narrow, 14" by 4-^". 



All the specimens appear to agree with that described by Wall in having surfaces for 

 the direct attachment of the cartilages of four pairs of ribs — the first to the anterior 

 corners (where the bone is broadest), the second to the junction of the ankylosed first 

 and second pieces of the sternum, the third to the hinder end of the second piece, and 

 the fourth to the third piece, or, in the Caithness skeleton, to the cartilaginous mass in 

 which this is imbedded. 



The sternum of the Cachalot resembles that of its nearest congeners, Hyperoodon and 

 Ziphius, in general principle of construction, being formed from three pairs of ossific 



