".] THE SPINAL SKELETON. 61 



In lower forms, e.g. Tailed-Batrachians and Fishes, the 

 inferior (hypapophysial) arches sometimes develop articular 

 processes or parts simulating such. 



31. The beautiful sigmoid curvature of the VERTEBRAL 

 COLUMN of man (Fig. 38) is, in its perfection, absolutely pecu- 

 liar to him, though some of the Apes (not the highest, but the 

 Baboons Cynocephali] approximate to him in this respect. 

 This exceptional condition of structure in man is related to 

 his exceptional (erect) attitude. 



As exceptional a curvature, though a very different one, 

 may exist. This is shown "by Bats, where the hinder part 

 of the spine bends sharply forwards as a quadrant, bringing 

 the pelvis very much in front. 



The gradual thickening of the spinal axis from its cranial 

 end downwards to the sacrum, is a condition which obtains 

 generally in Vertebrates, except Fishes, Bats, and those 

 extinct flying Saurians the Pterodactyles, in which that axis 

 gradually decreases in bulk tailwards. 



The post-axial projection of the neural spines, especially 

 those of the posterior cervical and anterior dorsal vertebrae, is 

 considerably less in man than in most animals of his class, 

 though considerably greater than in some e.g. the Hedgehog. 

 On the other hand, neural spines attain in many Fishes (e.g. the 

 Sole, Turbot, &c.) a prolongation compared with the size of 

 the spinal axis vastly exceeding anything to be found even 

 in the marine (Cetacean) members of the class to which man 

 belongs. 



32. The mode of OSSIFICATION of the vertebrae of man 

 agrees with that which exists generally in his class, most of 

 the vertebrae ossifying from one point in the body and one 

 other point in each neural arch besides from the epiphyses, 

 where these exist. 



The line of junction of the lateral (neural) pieces with the 

 central piece is termed the neuro-central suture, and in most 

 Mammals, as in man, it is so disposed that each lateral piece 

 contributes to form a portion of the body. This is not, how- 

 ever, universally the case, as in the Whale order the suture 

 is placed more dorsally, so that the central ossification forms 

 not only all the centrum, but also more or less of each lateral 

 piece. 



Just as in man, so in other members of his class, separate 

 ossifications often indicate costal elements in the cervical, 

 lumbar, and sacral regions. 



The fact, however, of a part being ossified by the extension 



