512 DR. J. MUBIE ON THE ANATOMY OF THE SEA-LION. 



between them being less pronounced. The rib at the angle has lost the semi-twist 

 possessed by the sixth ; but instead there is a more regular spiral, so that the outer 

 surface has a somewhat backward inclination below. The sternal extremity is thinned. 

 Surface within and without body biconvex, with sharp antero-posterior edges. 



The 13th, 14th, and 15th ribs have little or no distinction between head, neck, and 

 tubercle; they are elliptical in their long diameter, weak, slightly concave in arch, 

 the free extremities tapering. They all articulate, with but a single vertebral body. 

 The zygapophysial articulating surface is on their inner sides. Instead of a convex 

 angle there is a shallow concavity in its place, which is very slight in the 13th, a 

 little more so in the 14th, and distinct in the 15th. 



c. Sternum. — De Blainville's representation of this bone ('Atlas,' i. ii. pi. vii.) 

 calls for a few remarks on my part. These refer to the intersternal and superadded 

 cartilaginous elements. As the above authority shows, there are eight sternal 

 bones, the manubrium being prolonged beyond the first rib ; but the attached rib- 

 cartilages are nine in number. In these respects the Society's specimen agrees. De 

 Blainville's more aged animal and dry skeleton, however, have misled him — first, in 

 assigning too limited an area for the intersternal cartilages ; secondly, in the abutment 

 of the eighth and ninth sternal ribs against the seventh bone instead of behind 

 it on the cartilage ; and, thirdly, in the xiphoid cartilage being narrow and straight, 

 instead of spatulate. These omissions, through a defective skeleton, have to some 

 extent been already rectified from the present specimen, by my friend Mr. Parker'. 

 The manubrium has a flat dorsal and carinate ventral surface, the anterior broader 

 segment terminating in a forwardly projecting blunt cartilage an inch long. The pos- 

 terior segment is much narrower, stouter, and vertically deeper than the anterior 

 portion. The second, third, fourth, fifth, and sixth meso-sternal elements range about 

 one size, and differ from each other chiefly as regards breadth and thickness. From 

 being round, with bulbous extremities, they gradually alter, becoming broader, thinner, 

 and flatter. The seventh piece is unlike the sixth in having an arched instead of trun- 

 cate posterior extremity, the rounded edges thus giving greater space to the inter 

 sternal cartilage, whereby, as aforesaid, the eighth and ninth sternal ribs join it. 



The " metosteon " of the xiphoid precisely resembles one of the phalanges of the 

 manus, but is thinner ; the xipho-cartilage has a short narrow handle, ending in a broad 

 rounded extremity, not quite pyriform, as Parker remarks, and certainly entirely 

 different from De Blainville's figure. 



The several bones from the prse- to the xiphosternum measure respectively 2*8, T6, 

 T4, 1*3, T4, T5, T9, 2*5 inches long. In a young female of the same species which I 

 have had an opportunity of comparing, these bones had the following long diameters 



1 A Monograph of the Structure and Development of the Shoulder-girdle and Sternum in the Vertebrata 

 (Kay Soc. 1S67), p. 21 0, pi. xxx. fig. 7. Witness also fig. 25, pi. lxxii. of pt. ii. of my own memoir. 



