482 



APPLIED ANATOMY. 



The upper three vertebne can be palpated on their anterior surfaces by the finger 

 introduced into the mouth. 



Posteriorly the second, third, and fourth spines are too deeply placed between 

 the muscles to be palpated. 



To reduce the luxation an anaesthetic is given to relax the muscles, and cautious 

 extension is made and the head gently rotated. 



Fracture of the spine is frequently associated with luxation. It is most frequent 

 low down in the cervical region and at the junction of the dorsal and lumbar ver- 

 tebrae, these being the places where the 

 more fixed dorsal portion passes into the 

 more movable cervical and lumbar por- 

 tions (Fig. 485). The vertebrae are sup- 

 ported at three points the bodies and the 

 two articular processes. The spinous and 

 articular processes are rarely fractured 

 alone; they may be broken, however, by 

 direct violence. The laminae on each side 

 of the articular processes may be broken 

 and the detached part with the spinous 

 process may be pushed inward, injuring the 

 cord. Fracture of the bodies is most fre- 

 quent and is due to anterior flexion. The 

 bodies and intervertebral disks are com- 

 pressed, crushed, and torn. This is accom- 

 panied by either luxation or fracture of the 

 articular processes, and occurs most often 

 in the region of the lower dorsal vertebrae. 

 Injury to the cord is common. The parts 

 are not often fixed in a markedly displaced 

 position, as is the case with luxations of the 

 neck, hence attempts at reduction are rarely 

 necessary and fixation is to be aimed for in 

 treatment. The site of injury is determined 

 not only by an examination of the spinous processes but also by the extent of inter- 

 ference with the functions of the cord (see page 483). 



SPINAL CORD AND ITS MEMBRANES. 



The spinal cord in the male is 45 cm. (18 in.) long. In the foetus of three 

 months the cord extends to the end of the spinal canal; at birth it has risen to the 

 third lumbar vertebra, and in the adult it is opposite the lower border of the first. 

 It will thus be seen that the point of exit of the spinal nerves from the cord is always 

 some distance higher up than their exit from the intervertebral foramina. The cord 

 is enlarged in the cervical and lumbar regions, the cervical enlargement ending 

 opposite the second dorsal, and the lumbar enlargement beginning about opposite 

 the tenth dorsal vertebra and decreasing gradually. These enlargements correspond 

 with the origin of the nerves to the upper and lower extremities. 



The spinal cord is divided into so-called segments. These are thirty-one in 

 number ; eight are cervical, twelve thoracic, five lumbar, five sacral, and one coccy- 

 geal. Each segment embraces that portion of the cord which gives exit to one pair 

 of anterior or motor root fibres and receives one pair of posterior or sensory root 

 fibres. These segments are a variable distance above the point of exit of the nerves 

 from the bony spinal column. Besides motor and sensory functions they exercise 

 control over certain reflex movements and functions. The control of the bladder and 

 rectum is located in the fifth and sixth sacral segments; the cremasteric reflex is gov- 

 erned by the first and second lumbar ; the plantar or Babinski reflex by the first to 

 third sacral, as is also ankle clonus; and the patella reflex by the second and third 

 lumbar segments. They likewise exert a trophic influence, and the appearing of 

 bed or pressure sores without ample cause is presumptive evidence of a spinal lesion 

 of the segments supplying the part. 



Pedicle 

 Articulation 



FIG. 485. Showing the method of articulation 

 of the eleventh and twelfth dorsal and the first and 

 second lumbar vertebrae. 



