394 A MANUAL OF ANATOMY. 



Its sections are generally cylindrical, except in the cervical 

 region, where they become slightly flattened from before 

 backward. It is divided into three regions, cervical (four 

 inches long), the dorsal (ten and one-half), and the lumbar 

 (the rest of the cord). In the first and third regions, the 

 cord is slightly enlarged and forms the cervical and lumbar 

 enlargements. 



The cervical enlargement extends from the third cervi- 

 cal to the second dorsal vertebra. The lumbar from the 

 ninth to the last dorsal or first lumbar vertebra. 



The cord is divided by two incomplete fissures into two 

 symmetrical halves. The central substance which con- 

 nects the halves of the cord is the commissure, and within 

 it is a minute canal, the central canal of the cord, which 

 opens into the fourth ventricle at the calamus scriptorius. 

 It is the remains of the central canal which extended through 

 the primitive cerebrospinal axis. 



The anterior fissure of the cord is a wider but shal- 

 lower fissure than the posterior, which is narrow and deep. 

 The first is one-third, the second one-half of the anteropos- 

 terior diameter of the cord. These fissures are co-ex- 

 tensive with the anterior and posterior fissures of the 

 medulla. 



The surface of the cord is further divided by two shallow 

 grooves the anterolateral and posterolateral, from which 

 issue the anterior and posterior nerve roots, into three 

 tracts, the anterior, lateral, and posterior. Here it is ap- 

 parent that the anterior tract is continuous with the pyra- 

 midal tract of the medulla, the lateral with the lateral, and 

 the posterior into the funiculi gracilis and cuneatus of the 

 medulla. 



On section, the characteristic arrangement of the white 

 and gray matter of the cord becomes apparent. The gray 



