NERVE-TISSUE. 285 



refraction and similar to the bodies found in the granular layers 

 of the retina. Their nature is unknown. 



The hypophysis cerebri exhibits two lobules, which are separated from each 

 other by a number of venous blood-vessels. The posterior small portion is 

 an elongation of the infundibulum, and probably belongs to the nervous struct- 

 ures. The anterior large lobule is a glandular formation, and, as Von Mihal- 

 kovits has demonstrated, was originally a club-like prolongation of the oral 

 cavity of the embryo. 



The pineal gland is attached to the brain by means of connective tissue, 

 and has no nerve elements in its interior. It is composed of alveoli, contain- 

 ing corpuscles in a reticular arrangement. In the middle portions, the alve- 

 oli are filled with the cerebral sand, consisting of globular or mulberry-like 

 concretions, as a rule exhibiting a concentric striation. 



The organic material in these bodies is infiltrated with carbonate of lime 

 and phosphate of magnesia. 



The gray substance of the spinal cord is in the center through- 

 out the whole length of the cord, reaching the greatest size in 

 the cervical and the lumbar portion, where the largest nerves for 

 the extremities arise. The general form of the gray substance in 

 tranverse section resembles a butterfly, the two anterior larger 

 wings being distinguished from the posterior smaller ones by a 

 shallow depression. Each half of the gray substance represents 

 a column, and the two are connected by commissures travers- 

 ing the so-called medullary cone or commissure leaf (Markblatt, 

 Commissurenblatt). (See Fig. 119.) 



Each gray column exhibits a large anterior, or motor, horn, 

 and a smaller posterior, or sensitive, horn. In the outer portion of 

 the anterior horn we find very large motor ganglionic elements, 

 varying greatly in size and shape in different portions of the 

 spinal cord. In some portions of the posterior horn ganglionic 

 elements are absent, and in their place accumulations of nuclei- 

 like bodies are observed. The posterior horn, from its soft con- 

 sistence, bears the unnecessary name, "gelatinous substance/' 

 which name by some histologists is given to the commissural 

 portions in the neighborhood of the central canal. The latter 

 portion is also called the central ependyma thread, or the central 

 gray nucleus. The central canal, a prolongation of the cerebral 

 ventricles, is lined by a columnar endothelium, which in youth 

 shows distinct cilia, while in older individuals the cilia are not so 

 plainly marked. 



(C) Ganglionic Elements. The ganglionic nerve elements (" gan- 

 glion cells ") are scattered throughout the gray substance of the 



