CONNECTIVE TISSUE. 



231 



termed " red medulla." With advancing age the medulla is 

 almost entirely transformed into fat-tissue, while the blood- 

 vessels decrease in number on account of the large proportion 

 of fat 5 it is then termed the " yellow medulla." 



THE RELATION OF THE SYSTEMS OF LAMELLAE TO 

 THE BLOOD-VESSELS.* 



The cortical substance of the shaft-bones of a newly born 

 pup is composed of trabeculae, which form a reticulum, elon- 

 gated in the longitudinal axis of the bone, the meshes being the 

 medullary spaces. The width of a trabecula is about the same 

 as the diameter of a neighboring medullary space. The trabecu- 

 lae are bone-tissue of a striated appearance, and contain flat 

 bone-corpuscles in a concentric arrangement. In the medullary 

 spaces we find the globular elements of the medulla closely 

 packed together with ramifying blood-vessels, principally in the 

 center. (See Fig. 90, and also Fig. 86.) 



FIG. 90. TIBIA OF A NEW-BORN DOG. TRANSVERSE SECTION. 

 CHROMIC ACID SPECIMEN. 



P, fibrous portion of the periosteum; SM, subperiosteal medullary layer; T, trabecula' 

 of bone ; M, medullary spaces. Magnified 25 diameters. 



In the compact substance of the bone of a dog about six 

 months old, the bulk of bone-tissue several times exceeds that of 

 the medullary tissue. We still meet with medullary spaces con- 

 taining blood-vessels and globular elements. Far more numer- 



* Translated from "Ueber die Eiick- und Neubildung von Blutgefassen im 

 Kiiochen und Knorpel." Wiener Mediz. Jahrb., 1873. 



