428 PEOFESSOB OWEN ON MACEOPUS. 



pressed. After the third dorsal the neural spines gradually become shorter and gain 

 in fore-and-aft breadth to the eleventh dorsal (fig. 10, d n, ns). In this vertebra a short 

 broad metapophysis (m) rises above the base of the prsezygapophysis, and clasps the 

 end of the postzygapophysis of the tenth dorsal. The neural spine (ns) becomes 

 vertical in the eleventh dorsal, indicating the centre of motion of this part of the 

 vertebral column. In the twelfth dorsal (ib. d 12), the metapophysis (m) suddenly gains 

 in size ; it is compressed, truncate, and exceeds the diapophysis (d) in length. The prse- 

 zygapophyses are represented by nearly vertical articular surfaces on the inner and fore 

 part of the base of the metapophysis. An anapophysial ridge (a) is developed from the 

 upper and back part of the diapophysis (d). In the thirteenth dorsal the anapophysis 

 (ib. fig. 10, D 13, a) projects backwards from the hind part of the neurapophysis as a 

 distinct process, five lines in length ; it clamps externally the base of the metapophysis 

 of the first lumbar. The convexity of the fore part and concavity of the hind part of 

 the centrum is retained in the second to the last of the dorsal series ; and in the large 

 hinder vertebrae of the present subject the articular surface is still supported by an 

 epiphysis, although the individual was fully mature, with completed and worn dentition 

 (PI. LXXIV.). The intraneural and epineural canals are present on one or both sides in 

 the hinder dorsals. In the last dorsal the diapophysial pits (PI. LXXV. fig. 10, d i3, d) 

 are the sole articulations retained for the last pair of ribs. 



Of the thirteen costal pairs, the first rib (PI. LXXVI. fig. 1) is the shortest and 

 thickest, and has the longest neck (c) in proportion to the body (d). The head (a) is 

 divided into two surfaces meeting at an acute angle; the tuberosity (b) is large and 

 convex. From that prominence to the distal end the outer border describes almost a 

 straight line ; the inner border curves fiom the head to the distal expansion ; the body 

 is slightly twisted. 



The second rib (ib. fig. 2) is the most bent ; its outer border near the tuberosity (l/) 

 inclines backward and makes the inner side of that part of the body concave. 



The remaining pairs are long and slender, especially so and with a strong curve 

 proximally in the middle pairs (ib. fig. 4), shorter and less curved in the hinder pairs 

 (ib. fig. 5). The " head " and " tubercle " are developed in aU. In the third rib (ib. fig. 3) 

 there is a depression on the upper part of the neck (c), not shown in the rest. The 

 seven anterior pairs of ribs articulate by cartilaginous hcemapophyses with the sternum, 

 which consists of six bones (sternebers, or haemal spines). 



The manubrium (ib. fig. 6) is subcarinate on the outer surface, broadest where it 

 gives attachment to the cartilages of the first pair of ribs, narrowing thence forward 

 to a point, and developing a pair of rough convexities (b, b) over the converging borders 

 for the clavicles ; it slightly expands at the narrower end (fig. 7), which has two half- 

 surfaces {b b) for the cartilages of the second pair of ribs, and a middle square surface («) 

 for the second sterneber. A long and expanded " xiphoid cartilage " succeeds the sixth 

 sterneber. 



