37G GENERAL ANATOMY. 



vascular. The first bony points appear in the places which 

 are most full of blood-vessels, under the form of isolated grains, 

 afterwards disseminated and collected into net-works. They 

 then form a lamina thin at the middle, and furnished with ra- 

 diating bony fibres at the circumference. The surfaces of the 

 bone are covered, and the intervals between the radiating 

 fibres are filled up, by a reddish and very vascular mucilagin- 

 ous substance. The pericranium and dura mater are still very 

 red and vascular at that period. 



595. The short or thick bones ossify in the same manner 

 as the extremities of the long bones. They are preceded in 

 their formation by cartilages which have the form, and ulti- 

 mately the volume of the bones which are to replace them. 

 These cartilages are at first homogeneous and full, and after- 

 wards present the successive changes already described: cavi- 

 ties, vascular membraneous canals, filled with viscous fluid, and 

 bony points which extend from the centre to the circumference. 



The patella and sesamoid bones are formed in a tissue which 

 is at first fibrous, then cartilaginous, and in the same manner 

 as the short bones. 



The mixed bones, are intermediate in their formation, as 

 they are in their external figure, and internal conformation, 

 between the bones of the two different classes. 



596. Many bones are formed by several distinct points of 

 ossification. 



Several median bones, whether broad or thick, are formed by 

 two lateral parts, which afterwards unite in the median line. Of 

 this kind are the arches of the vertebrae, the frontal bone, the 

 body of the sphenoid bone, the squamous portion of the occi- 

 pital bone, the inferior maxillar bone, and the middle pieces of 

 the sternum. But in several of the median bones also, ossifi- 

 cation commences at the middle, and extends towards the 

 sides, as in the body of the vertebrae, the basilar portion of 

 the occipital bone, the crest of the ethmoid bone, the body of 

 the hyoid bone, and the first and last bones of the sternum, 

 whether the bone is formed of two lateral portions at an earlier 

 period, at the period of its conversion into cartilage, for exam- 

 ple, or whether it be originally single. 



