PRENATAL GROWTH OF SPINAL CORD 55 



The 11 mm. cord in general tapers from the cervical end to the 

 caudal extremity. In the 65 mm. and the 150 mm. stages the 

 cervical and lumbar enlargements appear very prominent. 



2. The percentage which the spinal cord forms of the entire 

 body declines rapidly during the second and third months of 

 prenatal life and later more slowly, as shown by Jackson. The 

 actual rate of absolute growth of the cord is much more rapid 

 during the early prenatal months than during the later periods. 



3. The various regions of the cord form different percentages 

 of the whole cord at different ages. The cervical region forms 

 approximately 37 per cent of the whole cord in the 11 mm. em- 

 bryo and decreases to 28 per cent in the mid-fetal stage (150 mm.). 

 In the child and adult it forms 36 per cent and 31 per cent of the 

 whole, respectively. In the thoracic region there is a gradual 

 increase from 32 per cent in the 11 mm. embryo to 41 per cent 

 in the (150 mm.) mid-fetal stage, to 45 per cent in the child, and 

 50 per cent in the adult. The lumbo-sacral region of the cord 

 increases relatively from 31 per cent in the 11 mm. embryo to a 

 maximum of 38 per cent at 31 mm. This is followed by a gradual 

 decrease to 31 per cent in the mid-fetal stage and to 18 per cent 

 in both child and adult. This decrease in relative size which 

 occurs from the second month of prenatal life and extends into 

 the postnatal period, is associated with the shortening of the cord 

 in the vertebral canal. It is very remarkable when compared 

 with the relative increase at the same time in the corresponding 

 portions of the body (pelvis and lower extremities). This de- 

 crease is most marked in the sacral region of the cord. The 

 thoracic region appears to grow at the expense of the cervical 

 region up to about the second month of prenatal life, and there- 

 after at the expense of the lumbo-sacral region, continuing up 

 to the adult cord. 



4. The gray matter constitutes about 38 per cent of the whole 

 cord in the 11 mm. embryo increasing relatively to about 58 per 

 cent in the 65 mm. specimen. Thereafter it decreases until in 

 the child it forms 27 per cent and in the adult less than 20 per 

 cent of the whole cord. The relative amount of gray matter in 

 the cervical region from the earliest stages, and in the lumbo- 



THB JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 23, NO. 1 



