THE SPINAL CORD 767 



a capital H, the cross-bar of the letter being formed by the gray commissure. 

 Each lateral part is considered as consisting of dorsal and ventral gray .columns 

 (Columna grisea dorsalis, ventralis), which appear in cross-section as the so-called 

 horns (Cornu dorsale, ventrale) . In the greater part of the cord the dorsal column 

 or horn is elongated and narrow and tapers to a point which extends almost to the 

 surface of the cord at the attachment of the dorsal root-fibers of the spinal nerves. 

 Its apex or tip consists of gray matter which is lighter in color and less opaque 

 than that of the rest of the horn, and is termed the substantia gelatinosa. The 

 ventral column or horn is short, thick, and rounded, and is separated from the surface 

 of the cord by a thick layer of white matter, through which the fibers of the ventral 

 roots of the spinal nerves pass. From the middle of the cervical region to the 

 lumbar region there is a medial projection of gray matter on the ventral part of the 

 dorsal column; this is the nucleus dorsalis. ^ In the anterior part of the cord there 

 is an outward projection of the gray matter at the base of the ventral horn; this 

 is termed the lateral column or horn. The demarcation between the gray and 

 white matter is in many places indistinct; this is especially the case laterally, 

 where processes of gray matter extend into the white substance, producing what 

 is known as the formatio reticularis. 



Cross-sections of the spinal cord present the following gross regional characters: (1) The 

 cervical cord near the medulla is compressed dorso-ventrally. Its width is about 18 mm. and 

 its greatest thickness about 8 mm. It has dorsally a deep median sulcus and a distinct dorso- 

 lateral sulcus. Lateral grooves are also present. The dorsal cornua are strongly everted. Each 

 has an expanded head, which comes very close to the surface of the cord, and has an extensive 

 cap of substantia gelatinosa. The neck is distinct. The ventral cornua are short and blunt and 

 diverge very little. The gray commissure is about in the middle of the section, and 2.5 mm. 

 in length. According to Dexler, the column between the median and lateral grooves dorsally 

 is the funiculus cmieatus, the funiculus gracilis being very small and not showing on the surface 

 in this region. In the middle of the cervical region the diameters are about 16 mm. and 10 mm. 

 respectively. The ventral surface is somewhat flattened. The dorsal cornua have pointed ends 

 and turn decidedly outward. The ventral cornua are short and thick and are directed very slightly 

 outward; their ends are about 4 mm. from the ventral surface. The gray commissure is just 

 above the middle of the section and is about 2 mm. long. The cervical enlargement measures 

 about 25 mm. transversely and 12 inm. vertically. The dorsal cornua are smaller than the ventral 

 and have a large cap of substantia gelatinosa. The ventral cornua are short and thick, curve 

 strongly outward, and are about 4 mm. from the ventral surface. Each bears a prominence on its 

 medial side near the base. The gray commissure is considerably above the middle of the section 

 and is about 4 mm. long. (2) In the middle of the thoracic region the cross-section is biconvex, 

 the ventral surface being the more strongly curved. The transverse diameter is about 15 mm. 

 and the dorso-ventral about 10 mm. The gray columns are close together, the gray commissure 

 being only about 1 mm. in length, and lying considerably above the middle of the section. The 

 dorsal cornua are short and have slightly enlarged ends. The ventral cornua have a uniform diame- 

 ter, tm^ very little outward, and end about 3 mm. from the ventral surface. (3) The lumbar enlarge- 

 ment is much flattened, especially dorsally. The transverse diameter is about 22 mm. and the 

 dorso-ventral 9 to 10 mm. The cornua are very large. The ventral cornua are thick and rounded 

 and turn sharply outward; they end about 2 mm. from the ventral surface. The dorsal cornua 

 are smaller and shorter and do not diverge so strongly. The gray commissure is about in the 

 middle of the section and is about 3 mm. long. In the third lumbar vertebra the cord is about 

 3 mm. narrower and thicker, and both surfaces are about equally convex. The dorsal cornua are 

 smaller, considerably everted, and constricted in the middle. The ventral cornua are very short 

 and do not turn outward. (4) In the first sacral vertebra the cord is almost round and is 5 to 6 mm. 

 in diameter; the cornua are relatively very large and the commissure has the form of a high inter- 

 mediate mass. 



The ventral horn contains large cells, the axones of which emerge as the fibers of the ventral 

 nerve-roots (Fila radicularia). The axones of many cells cross to the opposite side in the white 

 commissure and pass out in a ventral root of that side, or enter the white matter and pass forward 

 and backward, associating various segments of the cord. Some pass to the ventral horn of the 

 opposite side at the same or at different levels. Others pass to the periphery of the cord, join 

 the cerebellospinal fasciculus, and extend to the cerebellum. Scattered through the gray matter 

 are many smaller cells with axones which pursue a short course and serve to connect different 

 parts of the gray matter. 



The white matter of the spinal cord is divided into three pairs of columns. 

 The dorsal columns (Funiculi dorsales) lie on either side of the dorsal median septum 

 and extend outward to the dorso-lateral groove and the dorsal gray column. The 



' Also known as Clarke's column. 



