MUSCULAR TlSnSUE. 107 



intra-uterine life ; others assign a considerably earlier period ; but owing to the 

 iincertainty that prevails as to the age of early emlnyos, the dates of commencing 

 ossification in the earliest bones cannot be given with precision. 



In regard to the number and arrangement of the osseous centres, the following 

 general facts may be stated : — 1. In the long bones there is one centre of ossifi- 

 cation in the middle, and the ends are for the most part ossified from separate 

 centres ; whilst a \ajev of cartilage remains intcriiosed untO. the bone has nearly 

 attained its full length. By this means the Ijone is indui'ated in the parts where 

 streng-th is most required, whilst its longitudinal growth is facilitated. 2. The 

 larger foramina and ca%'ities of the skeleton are for the most part fonned by the 

 junction of two. but more generally of three or more ossific centres around the 

 apertiue or included space. The vertebral rings, the acetabulum, the occipital 

 foramen, and the cranium itself, are illustrations of this. It is easy to conceive 

 that in this way the ready and equable enlargement of such cavities and apertiu'cs 

 is provided for. 3. Bones of a complex figure, like the vertebriu. have usually 

 many centres of ossification ; but the converse is not always tnie. 4. "We can 

 frequentlj' connect the number of ossific centres with the principle of unifonnity 

 of tyi>e on which the skeleton of vertel)rated animals is constructed. Thus the 

 tTti)ical fonn of the sternum seems to be that of a series of distinct bones, one 

 placed between each pair of ribs in front, as the vertebra) are behind, and this 

 is its permanent condition in many quadrupeds. In man it confonns to the 

 general type in its mode of formation, in so far as it is ossified from several 

 centres, and for some time consists of several pieces ; but, to suit the fabric of 

 the human thorax, these at last coalesce one with another, and are reduced in 

 number to three. 



Reg-eneration of Bone. — In the reunion of fractured bones, osseous matter 

 is formed between and around the broken end.s, connecting them finnlj^ together ; 

 and when a portion of bone dies, as happens in necrosis, a growth of new bone 

 very generally takes place to a greater or less extent, and the dead part is 

 thrown off. The several steps of the process of restoration in these instances 

 are so fully described in works on Surgical Pathology, that it is unnecessaiy to 

 add to the leng-th of this chapter by introducing an account of them liere. 

 Nevertheless it may be well to refer brietiy to the importance of the periosteum 

 in the process of repair, a point that was urged by Duliamel and Troja. and 

 more recently by Syme and Oilier.* It is well known that if a portion of 

 periosteum be stripped off, the subjacent bone will )je liable to die and ex- 

 foliate ; conversely, if a large part or the whole of a bone be removed and the 

 periosteum at the same time be left intact, the bone will, in a great measure, be 

 regenerated. These and many other facts connected with the subject of osseous 

 regeneration have been very fully illustrated by the experiments of Oilier, 

 who has sho^\^^, amongst other things, that osseous fonnation will even occur in 

 connection with piortions of i^eriosteum which have been strijiped away from the 

 bone itself and intertwined amongst the muscles of the part, or even with 

 portions that have been entirely removed from a bone and transplanted to a 

 soft tissue — as, for instance, underneath the skin. 



MUSCUIiAE. TISSUE. 



The muscular tissue is that by means of which the active movements 

 of the body are produced. It consists of fine fibres, which are for the 

 most part collected into distinct organs called muscles, and in this form 

 it is familiarly known as the flesh of animals. These fibres are also 

 disposed round the sides of cavities and between the coats of hollow 

 viscera, forming strata of greater or less thickness. The muscular 

 fibres are endowed with contractilify, a remarkable and characteristic 

 property, by virtue of which they shrink or contract more or less 

 rapidly under the influence of certain causes which are capable of 



* Syme, Trans. K. S. Ed. 1840. Oilier, Traite de la Eegeneration des Os. Paris, 18G7. 



