Introduction to Animal Morphology. ig 



secondary areolse. In this case the bone columns are usually 

 arranged so as to give the greatest strength consistent with 

 the amount of solid material.* 



Within growing bone the unossified nucleated protoplasm, 

 formed by the proliferation of cartilage cells, becomes the 

 marrow, of which there are three kinds : yellow, gelatinous, 

 and red. The first consists of delicate connective tissue, ves- 

 sels and fat cells, and fills the shafts of long bones in most 

 Mammalia. The second form consists of an abundant trans- 

 lucent tissue (coagulable by acetic acid), and a few free nu- 

 cleated cells. The third form consists of a stroma of stellate 

 corpuscles entangling lymph cells, and surrounded by a close 

 capillary network of blood-vessels whose calibre is four times 

 greater than that of its feeding arteries. By the proliferation 

 of smaller cells, large colossal (myeloid) cells and polynuclear 

 masses (myeloplaxes) are formed. f In this tissue found in 

 the cancelli of young bone, Naumann, Bizzozero, and others 

 suppose the red blood corpuscles to be formed. (Red marrow 

 is sparingly present in birds.) 



Bones may be long, flat, or irregular ; they constitute the 

 sclerome or skeleton. Those developed in the integument 

 are called exoskeletal, those in an internal cartilage basis 

 form the endoskeleton, which consists of rst, an axial or 

 central column protecting the nervous and visceral systems, 

 and 2nd, an appendicular part, or the skeleton of the limbs. 

 Dermal or integumental bones are developed by ossification 

 in a fibrous matrix (parostosis], and have no granular stage. 

 Endoskeletal bones may be developed by endostosis (ossifica- 

 tion beginning within the intercellular spaces of a rartilago 

 mass), or by cctostosis (ossification proceeding from the sur- 

 inwards, beginning beneath the /v/v'/wAv/w or fibrous 

 sheath which surrounds all bones). 



li.stinfMiishes two sets of pillars in the cancelli, one set in 

 of K' ' 'iiicklinicn), and the other in the lii.e 



ul traction (traction lines, /.u^linicn). 



t />'' foinicd fVoni 



