372 



HUMAN PHYSIOLOGY 



vertebrae possess long processes to which 

 muscles of the back are attached. 

 Compare the vertebral column of the 

 frog and man in the following respects : 

 Is there a distinct neck region? Are 

 ribs present ? Are the ribs attached to 

 the vertebrae? How many vertebrae 

 in man bear ribs ? In man a flat bone 

 to which certain of the ribs are at- 

 tached is found on the ventral midline 

 of the skeleton. This bone, called the 

 sternum, is so small in the frog that you 

 will not be able to see it. Are all the 

 ribs in man attached to the breastbone 

 or sternum ? How many ribs are free 

 from the breastbone? Notice, in the 

 frog, the peculiar long bone at the pos- 

 terior end of the spinal column; this 

 bone is called the urostyle. No homol- 

 ogous bone is found in man. Look at 

 the vertebral column of man; notice 

 that it is shaped somewhat like the 

 letter S. The bodies of the vertebrae, 

 piled one upon the other, form a col- 

 umn of enough strength to support the 

 whole body. The double curve of the 

 vertebral column combines elasticity 

 with strength. 



Structure of a Vertebra in Man. — 

 Observe a single vertebra of man; it 

 will be found, in a general way, to con- 

 sist of two regions, a solid rounded por- 

 tion called the centrum or body, and a 

 bony arch from which are given off the 

 processes referred to above. Within 

 this arch (called the neural arch) is 

 found the spinal column or nerve cord. 

 Thus, the vertebrae form a wonderful 

 protection for this most delicate of all 

 organs; and, with the bony covering 

 of the skull, protect the central nervous 

 system. 



Skeleton of man; CR., cranium; CL., 

 clavicle; ST., sternum; SC, scapula; 

 H., humerus; V.C., vertebral column; 

 R., radius and ulna; P., pelvic girdle; 

 C, carpals; MC, metacarpals; Ph., 

 phalanges; F., femur; Fi., fibula; T. 

 tibia; Tar., tarsals; MT., metatarsals. 



Adaptations in the Vertebral 

 Column. — The vertebral column 

 in man is made up of many sepa- 

 rate pieces of bone: thirty-three 

 in a child; twenty-six in the adult, 

 several bones in the region of the pelvis later growing together. 

 Each vertebra presents the general form of a body or centrum of 

 bone and a bony arch with seven projections; in this arch runs 



