THE CHIMPANZEES AND ORANGS. 103 



trum is greater, and the upper and lower costal surfaces are less equal and less approxi- 

 mated than in the Chimpanzee. 



The neural spines of the eighth and the preceding dorsal vertebrae are shorter than in 

 the Gorilla and also than in the Chimpanzee ; they are thicker transversely and less 

 extended in the axis of the spine, especially at their extremities, which are tuberous, 

 not truncate as in the Chimpanzee. 



In the ninth dorsal vertebra {ib. 9 ) the centrum is relatively larger, and the accessory 

 tubercle above the diapophysis is more produced. 



The tenth dorsal vertebra {ib. lo, & figs. 4, 6 & 8) chiefly diflfers from the preceding 

 in the absence of the lower costal surface on each side, as at pi, fig. 4, in which it agrees 

 with the tenth dorsal of the Chimpanzee and differs from that in the Gorilla. 



In the eleventh dorsal vertebra the metapophysial tubercle (m) which was slightly 

 indicated in the preceding vertebra becomes more distinct. The centrum continues 

 to increase in size. 



In the twelfth dorsal vertebra (fig. 2, 12) the centrum continues to enlarge, and the 

 neural spine to gain in vertical extent. The metapophyses are well developed : the 

 anapophyses (a) may be recognized distinctly : the diapophyses are reduced to smooth 

 tubercles without an articular facet. The neural arch of this vertebra contracts in 

 breadth below, concomitantly with the modified shape and direction of the lower zyg- 

 apophyses (/), which are elongated and incline more obliquely outward than in the pre- 

 ceding vertebra. This modification does not characterize the corresponding vertebra 

 in the Gorilla or Chimpanzee. The upper emargination of the neural arch is wider in 

 the twelfth dorsal, which is distinguishable from the eleventh not only by this character, 

 but by the distinctness and greater length of the metapophyses, and by the greater length 

 and minor breadth of the part of the neural arch supporting the lower zygapophyses. 



Lumbar Vertebra (PL XXXV.). — These in the Gorilla and Chimpanzee are four in 

 number, by reason of the retention of distinct or free pleurapophyses in the vertebra 

 answering to the first lumbar in Man : they are, also, in some adults of both Gorilla 

 and Chimpanzee, further reduced by the modification of the vertebra answering to the 

 last lumbar in Man, by which it assumes the characters of a sacral vertebra. 



In the full-grown but not old male Gorilla in the Museum of the Royal College of 

 Surgeons, the four lumbar vertebrre are distinct. 'J'hey are figured in PI. XXXV. fig. 1 , 

 and have longer bodies in proportion to their breadth than in Man ; their spines slope 

 more downwards, are more expanded at their extremities, and in all but the last are sub- 

 bifid, in the Gorilla. The metapophyses (m) continue more distinct and prominent. 



When naturally articulated together, they form a straight line, without any tendency 

 to convexity forwards as in Man ; and the whole series of true vertebrae in the Gorilla 

 form but one curvature which is slightly concave forwards, especially in the dorsal region. 



In the first lumbar vertebra (PI. XXXV. fig. 1 , i ) the metapophysis (m) is still large 

 and distinct ; the upper zygapophysis becomes more convex and oblique in position ; the 



